diff --git a/framework/CHANGELOG.md b/framework/CHANGELOG.md
index 14eb2e62a6..ea764b1814 100644
--- a/framework/CHANGELOG.md
+++ b/framework/CHANGELOG.md
@@ -68,6 +68,7 @@ Yii Framework 2 Change Log
 - Enh #3132: `yii\rbac\PhpManager` now supports more compact data file format (qiangxue)
 - Enh #3154: Added validation error display for `GridView` filters (ivan-kolmychek)
 - Enh #3196: Masked input upgraded to use jquery.inputmask plugin with more features. (kartik-v)
+- Enh #3220: Added support for setting transation isolation levels (cebe)
 - Enh #3222: Added `useTablePrefix` option to the model generator for Gii (horizons2)
 - Enh #3230: Added `yii\filters\AccessControl::user` to support access control with different actors (qiangxue)
 - Enh #3232: Added `export()` and `exportAsString()` methods to `yii\helpers\BaseVarDumper` (klimov-paul)
diff --git a/framework/db/Connection.php b/framework/db/Connection.php
index a9638e7c22..1388837281 100644
--- a/framework/db/Connection.php
+++ b/framework/db/Connection.php
@@ -410,16 +410,18 @@ class Connection extends Component
 
     /**
      * Starts a transaction.
+     * @param string|null $isolationLevel The isolation level to use for this transaction.
+     * See [[Transaction::begin()]] for details.
      * @return Transaction the transaction initiated
      */
-    public function beginTransaction()
+    public function beginTransaction($isolationLevel = null)
     {
         $this->open();
 
         if (($transaction = $this->getTransaction()) === null) {
             $transaction = $this->_transaction = new Transaction(['db' => $this]);
         }
-        $transaction->begin();
+        $transaction->begin($isolationLevel);
 
         return $transaction;
     }
diff --git a/framework/db/Schema.php b/framework/db/Schema.php
index 57207345ec..a2c7bfda94 100644
--- a/framework/db/Schema.php
+++ b/framework/db/Schema.php
@@ -339,6 +339,19 @@ abstract class Schema extends Object
         $this->db->createCommand("ROLLBACK TO SAVEPOINT $name")->execute();
     }
 
+    /**
+     * Sets the isolation level of the current transaction.
+     * @param string $level The transaction isolation level to use for this transaction.
+     * This can be one of [[Transaction::READ_UNCOMMITTED]], [[Transaction::READ_COMMITTED]], [[Transaction::REPEATABLE_READ]]
+     * and [[Transaction::SERIALIZABLE]] but also a string containing DBMS specific syntax to be used
+     * after `SET TRANSACTION ISOLATION LEVEL`.
+     * @see http://en.wikipedia.org/wiki/Isolation_%28database_systems%29#Isolation_levels
+     */
+    public function setTransactionIsolationLevel($level)
+    {
+        $this->db->createCommand("SET TRANSACTION ISOLATION LEVEL $level;")->execute();
+    }
+
     /**
      * Quotes a string value for use in a query.
      * Note that if the parameter is not a string, it will be returned without change.
diff --git a/framework/db/Transaction.php b/framework/db/Transaction.php
index f524604d82..39a2e47b38 100644
--- a/framework/db/Transaction.php
+++ b/framework/db/Transaction.php
@@ -38,6 +38,27 @@ use yii\base\InvalidConfigException;
  */
 class Transaction extends \yii\base\Object
 {
+    /**
+     * A constant representing the transaction isolation level `READ UNCOMMITTED`.
+     * @see http://en.wikipedia.org/wiki/Isolation_%28database_systems%29#Isolation_levels
+     */
+    const READ_UNCOMMITTED = 'READ UNCOMMITTED';
+    /**
+     * A constant representing the transaction isolation level `READ COMMITTED`.
+     * @see http://en.wikipedia.org/wiki/Isolation_%28database_systems%29#Isolation_levels
+     */
+    const READ_COMMITTED = 'READ COMMITTED';
+    /**
+     * A constant representing the transaction isolation level `REPEATABLE READ`.
+     * @see http://en.wikipedia.org/wiki/Isolation_%28database_systems%29#Isolation_levels
+     */
+    const REPEATABLE_READ = 'REPEATABLE READ';
+    /**
+     * A constant representing the transaction isolation level `SERIALIZABLE`.
+     * @see http://en.wikipedia.org/wiki/Isolation_%28database_systems%29#Isolation_levels
+     */
+    const SERIALIZABLE = 'SERIALIZABLE';
+
     /**
      * @var Connection the database connection that this transaction is associated with.
      */
@@ -47,6 +68,7 @@ class Transaction extends \yii\base\Object
      */
     private $_level = 0;
 
+
     /**
      * Returns a value indicating whether this transaction is active.
      * @return boolean whether this transaction is active. Only an active transaction
@@ -59,9 +81,15 @@ class Transaction extends \yii\base\Object
 
     /**
      * Begins a transaction.
+     * @param string|null $isolationLevel The [isolation level][] to use for this transaction.
+     * This can be one of [[READ_UNCOMMITTED]], [[READ_COMMITTED]], [[REPEATABLE_READ]] and [[SERIALIZABLE]] but
+     * also a string containing DBMS specific syntax to be used after `SET TRANSACTION ISOLATION LEVEL`.
+     * If not specified (`null`) the isolation level will not be set explicitly and the DBMS default will be used.
+     *
+     * [isolation level]: http://en.wikipedia.org/wiki/Isolation_%28database_systems%29#Isolation_levels
      * @throws InvalidConfigException if [[db]] is `null`.
      */
-    public function begin()
+    public function begin($isolationLevel = null)
     {
         if ($this->db === null) {
             throw new InvalidConfigException('Transaction::db must be set.');
@@ -69,7 +97,10 @@ class Transaction extends \yii\base\Object
         $this->db->open();
 
         if ($this->_level == 0) {
-            Yii::trace('Begin transaction', __METHOD__);
+            if ($isolationLevel !== null) {
+                $this->db->getSchema()->setTransactionIsolationLevel($isolationLevel);
+            }
+            Yii::trace('Begin transaction' . ($isolationLevel ? ' with isolation level ' . $isolationLevel : ''), __METHOD__);
             $this->db->pdo->beginTransaction();
             $this->_level = 1;
 
@@ -141,4 +172,25 @@ class Transaction extends \yii\base\Object
             throw new Exception('Roll back failed: nested transaction not supported.');
         }
     }
+
+    /**
+     * Sets the transaction isolation level for this transaction.
+     *
+     * This method can be used to set the isolation level while the transaction is already active.
+     * However this is not supported by all DBMS so you might rather specify the isolation level directly
+     * when calling [[begin()]].
+     * @param string $level The transaction isolation level to use for this transaction.
+     * This can be one of [[READ_UNCOMMITTED]], [[READ_COMMITTED]], [[REPEATABLE_READ]] and [[SERIALIZABLE]] but
+     * also a string containing DBMS specific syntax to be used after `SET TRANSACTION ISOLATION LEVEL`.
+     * @throws Exception if the transaction is not active
+     * @see http://en.wikipedia.org/wiki/Isolation_%28database_systems%29#Isolation_levels
+     */
+    public function setIsolationLevel($level)
+    {
+        if (!$this->getIsActive()) {
+            throw new Exception('Failed to set isolation level: transaction was inactive.');
+        }
+        Yii::trace('Setting transaction isolation level to ' . $level, __METHOD__);
+        $this->db->getSchema()->setTransactionIsolationLevel($level);
+    }
 }
diff --git a/framework/db/sqlite/Schema.php b/framework/db/sqlite/Schema.php
index bcc83b5e51..eecdfc3161 100644
--- a/framework/db/sqlite/Schema.php
+++ b/framework/db/sqlite/Schema.php
@@ -7,8 +7,10 @@
 
 namespace yii\db\sqlite;
 
+use yii\base\NotSupportedException;
 use yii\db\TableSchema;
 use yii\db\ColumnSchema;
+use yii\db\Transaction;
 
 /**
  * Schema is the class for retrieving metadata from a SQLite (2/3) database.
@@ -249,4 +251,27 @@ class Schema extends \yii\db\Schema
 
         return $column;
     }
+
+    /**
+     * Sets the isolation level of the current transaction.
+     * @param string $level The transaction isolation level to use for this transaction.
+     * This can be either [[Transaction::READ_UNCOMMITTED]] or [[Transaction::SERIALIZABLE]].
+     * @throws \yii\base\NotSupportedException when unsupported isolation levels are used.
+     * SQLite only supports SERIALIZABLE and READ UNCOMMITTED.
+     * @see http://www.sqlite.org/pragma.html#pragma_read_uncommitted
+     */
+    public function setTransactionIsolationLevel($level)
+    {
+        switch($level)
+        {
+            case Transaction::SERIALIZABLE:
+                $this->db->createCommand("PRAGMA read_uncommitted = False;")->execute();
+            break;
+            case Transaction::READ_UNCOMMITTED:
+                $this->db->createCommand("PRAGMA read_uncommitted = True;")->execute();
+            break;
+            default:
+                throw new NotSupportedException(get_class($this) . ' only supports transaction isolation levels READ UNCOMMITTED and SERIALIZABLE.');
+        }
+    }
 }