diff --git a/project/build.scala b/project/build.scala
index 3b0cefb..c5cdd89 100644
--- a/project/build.scala
+++ b/project/build.scala
@@ -36,6 +36,7 @@
         "org.pegdown" % "pegdown" % "1.3.0",
         "org.apache.commons" % "commons-compress" % "1.5",
         "com.typesafe.slick" %% "slick" % "1.0.1",
+        "com.novell.ldap" % "jldap" % "2009-10-07",
         "com.h2database" % "h2" % "1.3.171",
         "ch.qos.logback" % "logback-classic" % "1.0.6" % "runtime",
         "org.eclipse.jetty" % "jetty-webapp" % "8.1.8.v20121106" % "container",
diff --git a/src/main/scala/app/SignInController.scala b/src/main/scala/app/SignInController.scala
index d7e8248..dea995a 100644
--- a/src/main/scala/app/SignInController.scala
+++ b/src/main/scala/app/SignInController.scala
@@ -1,7 +1,6 @@
 package app
 
 import service._
-import util.StringUtil._
 import jp.sf.amateras.scalatra.forms._
 
 class SignInController extends SignInControllerBase with SystemSettingsService with AccountService
@@ -24,19 +23,11 @@
   }
 
   post("/signin", form){ form =>
-    getAccountByUserName(form.userName).collect {
-      case account if(!account.isGroupAccount && account.password == sha1(form.password)) => {
-        session.setAttribute("LOGIN_ACCOUNT", account)
-        updateLastLoginDate(account.userName)
-
-        session.get("REDIRECT").map { redirectUrl =>
-          session.removeAttribute("REDIRECT")
-          redirect(redirectUrl.asInstanceOf[String])
-        }.getOrElse {
-          redirect("/")
-        }
-      }
-    } getOrElse redirect("/signin")
+    val settings = loadSystemSettings()
+    authenticate(loadSystemSettings(), form.userName, form.password) match {
+      case Some(account) => signin(account)
+      case None => redirect("/signin")
+    }
   }
 
   get("/signout"){
@@ -44,4 +35,19 @@
     redirect("/")
   }
 
+  /**
+   * Set account information into HttpSession and redirect.
+   */
+  private def signin(account: model.Account) = {
+    session.setAttribute("LOGIN_ACCOUNT", account)
+    updateLastLoginDate(account.userName)
+
+    session.get("REDIRECT").map { redirectUrl =>
+      session.removeAttribute("REDIRECT")
+      redirect(redirectUrl.asInstanceOf[String])
+    }.getOrElse {
+      redirect("/")
+    }
+  }
+
 }
\ No newline at end of file
diff --git a/src/main/scala/app/SystemSettingsController.scala b/src/main/scala/app/SystemSettingsController.scala
index 0e824c4..d1a813e 100644
--- a/src/main/scala/app/SystemSettingsController.scala
+++ b/src/main/scala/app/SystemSettingsController.scala
@@ -17,12 +17,22 @@
     "gravatar"                 -> trim(label("Gravatar", boolean())),
     "notification"             -> trim(label("Notification", boolean())),
     "smtp"                     -> optionalIfNotChecked("notification", mapping(
-        "host"     -> trim(label("SMTP Host", text(required))),
-        "port"     -> trim(label("SMTP Port", optional(number()))),
-        "user"     -> trim(label("SMTP User", optional(text()))),
-        "password" -> trim(label("SMTP Password", optional(text()))),
-        "ssl"      -> trim(label("Enable SSL", optional(boolean())))
-    )(Smtp.apply))
+        "host"                     -> trim(label("SMTP Host", text(required))),
+        "port"                     -> trim(label("SMTP Port", optional(number()))),
+        "user"                     -> trim(label("SMTP User", optional(text()))),
+        "password"                 -> trim(label("SMTP Password", optional(text()))),
+        "ssl"                      -> trim(label("Enable SSL", optional(boolean())))
+    )(Smtp.apply)),
+    "ldapAuthentication"       -> trim(label("LDAP", boolean())),
+    "ldap"                     -> optionalIfNotChecked("ldapAuthentication", mapping(
+        "host"                     -> trim(label("LDAP host", text(required))),
+        "port"                     -> trim(label("LDAP port", optional(number()))),
+        "bindDN"                   -> trim(label("Bind DN", text(required))),
+        "bindPassword"             -> trim(label("Bind Password", text(required))),
+        "baseDN"                   -> trim(label("Base DN", text(required))),
+        "userNameAttribute"        -> trim(label("User name attribute", text(required))),
+        "mailAttribute"            -> trim(label("Mail address attribute", text(required)))
+    )(Ldap.apply))
   )(SystemSettings.apply)
 
 
diff --git a/src/main/scala/service/AccountService.scala b/src/main/scala/service/AccountService.scala
index 3f828e3..39ddf6b 100644
--- a/src/main/scala/service/AccountService.scala
+++ b/src/main/scala/service/AccountService.scala
@@ -3,9 +3,48 @@
 import model._
 import scala.slick.driver.H2Driver.simple._
 import Database.threadLocalSession
+import service.SystemSettingsService.SystemSettings
+import util.StringUtil._
+import model.GroupMember
+import scala.Some
+import model.Account
+import util.LDAPUtil
 
 trait AccountService {
 
+  def authenticate(settings: SystemSettings, userName: String, password: String): Option[Account] =
+    if(settings.ldapAuthentication){
+      ldapAuthentication(settings, userName, password)
+    } else {
+      defaultAuthentication(userName, password)
+    }
+
+  /**
+   * Authenticate by internal database.
+   */
+  private def defaultAuthentication(userName: String, password: String) = {
+    getAccountByUserName(userName).collect {
+      case account if(!account.isGroupAccount && account.password == sha1(password)) => Some(account)
+    } getOrElse None
+  }
+
+  /**
+   * Authenticate by LDAP.
+   */
+  private def ldapAuthentication(settings: SystemSettings, userName: String, password: String) = {
+    LDAPUtil.authenticate(settings.ldap.get, userName, password) match {
+      case Right(mailAddress) => {
+        // Create or update account by LDAP information
+        getAccountByUserName(userName) match {
+          case Some(x) => updateAccount(x.copy(mailAddress = mailAddress))
+          case None    => createAccount(userName, "", mailAddress, false, None)
+        }
+        getAccountByUserName(userName)
+      }
+      case Left(errorMessage) => defaultAuthentication(userName, password)
+    }
+  }
+
   def getAccountByUserName(userName: String): Option[Account] = 
     Query(Accounts) filter(_.userName is userName.bind) firstOption
 
diff --git a/src/main/scala/service/SystemSettingsService.scala b/src/main/scala/service/SystemSettingsService.scala
index 6837f70..4c01135 100644
--- a/src/main/scala/service/SystemSettingsService.scala
+++ b/src/main/scala/service/SystemSettingsService.scala
@@ -19,6 +19,18 @@
         smtp.ssl.foreach(x => props.setProperty(SmtpSsl, x.toString))
       }
     }
+    props.setProperty(LdapAuthentication, settings.ldapAuthentication.toString)
+    if(settings.ldapAuthentication){
+      settings.ldap.map { ldap =>
+        props.setProperty(LdapHost, ldap.host)
+        ldap.port.foreach(x => props.setProperty(LdapPort, x.toString))
+        props.setProperty(LdapBindDN, ldap.bindDN)
+        props.setProperty(LdapBindPassword, ldap.bindPassword)
+        props.setProperty(LdapBaseDN, ldap.baseDN)
+        props.setProperty(LdapUserNameAttribute, ldap.userNameAttribute)
+        props.setProperty(LdapMailAddressAttribute, ldap.mailAttribute)
+      }
+    }
     props.store(new java.io.FileOutputStream(GitBucketConf), null)
   }
 
@@ -41,6 +53,19 @@
           getOptionValue[Boolean](props, SmtpSsl, None)))
       } else {
         None
+      },
+      getValue(props, LdapAuthentication, false),
+      if(getValue(props, LdapAuthentication, false)){
+        Some(Ldap(
+          getValue(props, LdapHost, ""),
+          getOptionValue(props, LdapPort, Some(DefaultLdapPort)),
+          getValue(props, LdapBindDN, ""),
+          getValue(props, LdapBindPassword, ""),
+          getValue(props, LdapBaseDN, ""),
+          getValue(props, LdapUserNameAttribute, ""),
+          getValue(props, LdapMailAddressAttribute, "")))
+      } else {
+        None
       }
     )
   }
@@ -54,8 +79,19 @@
     allowAccountRegistration: Boolean,
     gravatar: Boolean,
     notification: Boolean,
-    smtp: Option[Smtp]
-  )
+    smtp: Option[Smtp],
+    ldapAuthentication: Boolean,
+    ldap: Option[Ldap])
+
+  case class Ldap(
+    host: String,
+    port: Option[Int],
+    bindDN: String,
+    bindPassword: String,
+    baseDN: String,
+    userNameAttribute: String,
+    mailAttribute: String)
+
   case class Smtp(
     host: String,
     port: Option[Int],
@@ -63,6 +99,8 @@
     password: Option[String],
     ssl: Option[Boolean])
 
+  val DefaultLdapPort = 389
+
   private val AllowAccountRegistration = "allow_account_registration"
   private val Gravatar = "gravatar"
   private val Notification = "notification"
@@ -71,6 +109,14 @@
   private val SmtpUser = "smtp.user"
   private val SmtpPassword = "smtp.password"
   private val SmtpSsl = "smtp.ssl"
+  private val LdapAuthentication = "ldap_authentication"
+  private val LdapHost = "ldap.host"
+  private val LdapPort = "ldap.port"
+  private val LdapBindDN = "ldap.bindDN"
+  private val LdapBindPassword = "ldap.bind_password"
+  private val LdapBaseDN = "ldap.baseDN"
+  private val LdapUserNameAttribute = "ldap.username_attribute"
+  private val LdapMailAddressAttribute = "ldap.mail_attribute"
 
   private def getValue[A: ClassTag](props: java.util.Properties, key: String, default: A): A = {
     val value = props.getProperty(key)
diff --git a/src/main/scala/servlet/BasicAuthenticationFilter.scala b/src/main/scala/servlet/BasicAuthenticationFilter.scala
index 51d6618..6dda923 100644
--- a/src/main/scala/servlet/BasicAuthenticationFilter.scala
+++ b/src/main/scala/servlet/BasicAuthenticationFilter.scala
@@ -2,14 +2,13 @@
 
 import javax.servlet._
 import javax.servlet.http._
-import util.StringUtil._
-import service.{AccountService, RepositoryService}
+import service.{SystemSettingsService, AccountService, RepositoryService}
 import org.slf4j.LoggerFactory
 
 /**
  * Provides BASIC Authentication for [[servlet.GitRepositoryServlet]].
  */
-class BasicAuthenticationFilter extends Filter with RepositoryService with AccountService {
+class BasicAuthenticationFilter extends Filter with RepositoryService with AccountService with SystemSettingsService {
 
   private val logger = LoggerFactory.getLogger(classOf[BasicAuthenticationFilter])
 
@@ -58,12 +57,12 @@
     }
   }
 
-  private def isWritableUser(username: String, password: String, repository: RepositoryService.RepositoryInfo): Boolean = {
-    getAccountByUserName(username).map { account =>
-      account.password == sha1(password) && hasWritePermission(repository.owner, repository.name, Some(account))
-    } getOrElse false
-  }
-  
+  private def isWritableUser(username: String, password: String, repository: RepositoryService.RepositoryInfo): Boolean =
+    authenticate(loadSystemSettings(), username, password) match {
+      case Some(account) => hasWritePermission(repository.owner, repository.name, Some(account))
+      case None => false
+    }
+
   private def requireAuth(response: HttpServletResponse): Unit = {
     response.setHeader("WWW-Authenticate", "BASIC realm=\"GitBucket\"")
     response.sendError(HttpServletResponse.SC_UNAUTHORIZED)
diff --git a/src/main/scala/util/LDAPUtil.scala b/src/main/scala/util/LDAPUtil.scala
new file mode 100644
index 0000000..bb31f32
--- /dev/null
+++ b/src/main/scala/util/LDAPUtil.scala
@@ -0,0 +1,97 @@
+package util
+
+import service.SystemSettingsService.Ldap
+import service.SystemSettingsService
+import com.novell.ldap.{LDAPReferralException, LDAPEntry, LDAPConnection}
+
+/**
+ * Utility for LDAP authentication.
+ */
+object LDAPUtil {
+
+  private val LDAP_VERSION: Int = 3
+
+  /**
+   * Try authentication by LDAP using given configuration.
+   * Returns Right(mailAddress) if authentication is successful, otherwise  Left(errorMessage).
+   */
+  def authenticate(ldapSettings: Ldap, userName: String, password: String): Either[String, String] = {
+    bind(
+      ldapSettings.host,
+      ldapSettings.port.getOrElse(SystemSettingsService.DefaultLdapPort),
+      ldapSettings.bindDN,
+      ldapSettings.bindPassword
+    ) match {
+      case Some(conn) => {
+        withConnection(conn) { conn =>
+          findUser(conn, userName, ldapSettings.baseDN, ldapSettings.userNameAttribute) match {
+            case Some(userDN) => userAuthentication(ldapSettings, userDN, password)
+            case None => Left("User does not exist")
+          }
+        }
+      }
+      case None => Left("System LDAP authentication failed.")
+    }
+  }
+
+  private def userAuthentication(ldapSettings: Ldap, userDN: String, password: String): Either[String, String] = {
+    bind(
+      ldapSettings.host,
+      ldapSettings.port.getOrElse(SystemSettingsService.DefaultLdapPort),
+      userDN,
+      password
+    ) match {
+      case Some(conn) => {
+        withConnection(conn) { conn =>
+          findMailAddress(conn, userDN, ldapSettings.mailAttribute) match {
+            case Some(mailAddress) => Right(mailAddress)
+            case None => Left("Can't find mail address.")
+          }
+        }
+      }
+      case None => Left("User LDAP Authentication Failed.")
+    }
+  }
+
+  private def bind(host: String, port: Int, dn: String, password: String): Option[LDAPConnection] = {
+    val conn: LDAPConnection = new LDAPConnection
+    try {
+      conn.connect(host, port)
+      conn.bind(LDAP_VERSION, dn, password.getBytes)
+      Some(conn)
+    } catch {
+      case e: Exception => {
+        if (conn.isConnected) conn.disconnect()
+        None
+      }
+    }
+  }
+
+  private def withConnection[T](conn: LDAPConnection)(f: LDAPConnection => T): T = {
+    try {
+      f(conn)
+    } finally {
+      conn.disconnect()
+    }
+  }
+
+  private def findUser(conn: LDAPConnection, userName: String, baseDN: String, userNameAttribute: String): Option[String] = {
+    val results = conn.search(baseDN, LDAPConnection.SCOPE_SUB, userNameAttribute + "=" + userName, null, false)
+    (for(i <- 0 to results.getCount) yield try {
+      Some(results.next)
+    } catch {
+      case ex: LDAPReferralException => None // NOTE(tanacasino): Referral follow is off. so ignores it.(for AD)
+    }).flatten.collectFirst {
+      case x if(x != null) => x.getDN
+    }
+  }
+
+  private def findMailAddress(conn: LDAPConnection, userDN: String, mailAttribute: String): Option[String] = {
+    val results = conn.search(userDN, LDAPConnection.SCOPE_BASE, null, Array[String](mailAttribute), false)
+    if (results.hasMore) {
+      Option(results.next.getAttribute(mailAttribute)).map(_.getStringValue)
+    } else {
+      None
+    }
+  }
+}
diff --git a/src/main/twirl/account/edit.scala.html b/src/main/twirl/account/edit.scala.html
index 2eeb22a..24e0eaf 100644
--- a/src/main/twirl/account/edit.scala.html
+++ b/src/main/twirl/account/edit.scala.html
@@ -18,15 +18,17 @@
             <span id="error-userName" class="error"></span>
           </fieldset>
         }
-        <fieldset>
-          <label for="password"><strong>Password</strong>
-            @if(account.nonEmpty){
-              (Input to change password)
-            }
-          </label>
-          <input type="password" name="password" id="password" value=""/>
-          <span id="error-password" class="error"></span>
-        </fieldset>
+        @if(account.map(_.password.nonEmpty).getOrElse(true)){
+          <fieldset>
+            <label for="password"><strong>Password</strong>
+              @if(account.nonEmpty){
+                (Input to change password)
+              }
+            </label>
+            <input type="password" name="password" id="password" value=""/>
+            <span id="error-password" class="error"></span>
+          </fieldset>
+        }
         <fieldset>
           <label for="mailAddress"><strong>Mail Address</strong></label>
           <input type="text" name="mailAddress" id="mailAddress" value="@account.map(_.mailAddress)"/>
diff --git a/src/main/twirl/admin/system.scala.html b/src/main/twirl/admin/system.scala.html
index 9d8c9b6..5e9e794 100644
--- a/src/main/twirl/admin/system.scala.html
+++ b/src/main/twirl/admin/system.scala.html
@@ -8,6 +8,9 @@
       <div class="box">
         <div class="box-header">System Settings</div>
         <div class="box-content">
+          <!--====================================================================-->
+          <!-- Account registration -->
+          <!--====================================================================-->
           <label><strong>Account registration</strong></label>
           <fieldset>
             <label>
@@ -19,6 +22,9 @@
               <strong>Deny</strong> - Only administrators can create account.
             </label>
           </fieldset>
+          <!--====================================================================-->
+          <!-- Services -->
+          <!--====================================================================-->
           <hr>
           <label><strong>Services</strong></label>
           <fieldset>
@@ -27,6 +33,71 @@
               Gravatar
             </label>
           </fieldset>
+          <!--====================================================================-->
+          <!-- Authentication -->
+          <!--====================================================================-->
+          <hr>
+          <label><strong>Authentication</strong></label>
+          <fieldset>
+            <label>
+              <input type="checkbox" id="ldapAuthentication" name="ldapAuthentication"@if(settings.ldap){ checked}/>
+              LDAP
+            </label>
+          </fieldset>
+          <div class="form-horizontal ldap">
+            <div class="control-group">
+              <label class="control-label" for="ldapHost">LDAP Host</label>
+              <div class="controls">
+                <input type="text" id="ldapHost" name="ldap.host" value="@settings.ldap.map(_.host)"/>
+                <span id="error-ldap_host" class="error"></span>
+              </div>
+            </div>
+            <div class="control-group">
+              <label class="control-label" for="ldapPort">LDAP Port</label>
+              <div class="controls">
+                <input type="text" id="ldapPort" name="ldap.port" class="input-mini" value="@settings.ldap.map(_.port)"/>
+                <span id="error-ldap_port" class="error"></span>
+              </div>
+            </div>
+            <div class="control-group">
+              <label class="control-label" for="ldapBindDN">Bind DN</label>
+              <div class="controls">
+                <input type="text" id="ldapBindDN" name="ldap.bindDN" value="@settings.ldap.map(_.bindDN)"/>
+                <span id="error-ldap_bindDN" class="error"></span>
+              </div>
+            </div>
+            <div class="control-group">
+              <label class="control-label" for="ldapBindPassword">Bind Password</label>
+              <div class="controls">
+                <input type="password" id="ldapBindPassword" name="ldap.bindPassword" value="@settings.ldap.map(_.bindPassword)"/>
+                <span id="error-ldap_bindPassword" class="error"></span>
+              </div>
+            </div>
+            <div class="control-group">
+              <label class="control-label" for="ldapBaseDN">Base DN</label>
+              <div class="controls">
+                <input type="text" id="ldapBaseDN" name="ldap.baseDN" value="@settings.ldap.map(_.baseDN)"/>
+                <span id="error-ldap_baseDN" class="error"></span>
+              </div>
+            </div>
+            <div class="control-group">
+              <label class="control-label" for="ldapUserNameAttribute">User name attribute</label>
+              <div class="controls">
+                <input type="text" id="ldapUserNameAttribute" name="ldap.userNameAttribute" value="@settings.ldap.map(_.userNameAttribute)"/>
+                <span id="error-ldap_userNameAttribute" class="error"></span>
+              </div>
+            </div>
+            <div class="control-group">
+              <label class="control-label" for="ldapMailAttribute">Mail address attribute</label>
+              <div class="controls">
+                <input type="text" id="ldapMailAttribute" name="ldap.mailAttribute" value="@settings.ldap.map(_.mailAttribute)"/>
+                <span id="error-ldap_mailAttribute" class="error"></span>
+              </div>
+            </div>
+          </div>
+          <!--====================================================================-->
+          <!-- Notification email -->
+          <!--====================================================================-->
           <hr>
           <label><strong>Notification email</strong></label>
           <fieldset>
@@ -35,7 +106,7 @@
               Send notifications
             </label>
           </fieldset>
-          <div class="form-horizontal">
+          <div class="form-horizontal notification">
             <div class="control-group">
               <label class="control-label" for="smtpHost">SMTP Host</label>
               <div class="controls">
@@ -81,7 +152,11 @@
 <script>
 $(function(){
   $('#notification').change(function(){
-    $('.form-horizontal input').prop('disabled', !$(this).prop('checked'));
+    $('.notification input').prop('disabled', !$(this).prop('checked'));
+  }).change();
+
+  $('#ldapAuthentication').change(function(){
+    $('.ldap input').prop('disabled', !$(this).prop('checked'));
   }).change();
 });
 </script>
\ No newline at end of file
diff --git a/src/main/twirl/admin/users/user.scala.html b/src/main/twirl/admin/users/user.scala.html
index 98ae9ed..713d459 100644
--- a/src/main/twirl/admin/users/user.scala.html
+++ b/src/main/twirl/admin/users/user.scala.html
@@ -10,16 +10,18 @@
             <span id="error-userName" class="error"></span>
             <input type="text" name="userName" id="userName" value="@account.map(_.userName)"@if(account.isDefined){ readonly}/>
           </fieldset>
-          <fieldset>
-            <label for="password">
-              <strong>Password</strong>
-              @if(account.isDefined){
-                (Input to change password)
-              }
-            </label>
-            <span id="error-password" class="error"></span>
-            <input type="password" name="password" id="password" value="" autocomplete="off"/>
-          </fieldset>
+          @if(account.map(_.password.nonEmpty).getOrElse(true)){
+            <fieldset>
+              <label for="password">
+                <strong>Password</strong>
+                @if(account.isDefined){
+                  (Input to change password)
+                }
+              </label>
+              <span id="error-password" class="error"></span>
+              <input type="password" name="password" id="password" value="" autocomplete="off"/>
+            </fieldset>
+          }
           <fieldset>
             <label for="mailAddress"><strong>Mail Address</strong></label>
             <span id="error-mailAddress" class="error"></span>