diff --git a/src/Illuminate/Contracts/Database/Eloquent/CastsAttributes.php b/src/Illuminate/Contracts/Database/Eloquent/CastsAttributes.php
new file mode 100644
index 000000000000..4a12ce413e71
--- /dev/null
+++ b/src/Illuminate/Contracts/Database/Eloquent/CastsAttributes.php
@@ -0,0 +1,28 @@
+<?php
+
+namespace Illuminate\Contracts\Database\Eloquent;
+
+interface CastsAttributes
+{
+    /**
+     * Transform the attribute from the underlying model values.
+     *
+     * @param  \Illuminate\Database\Eloquent\Model  $model
+     * @param  string  $key
+     * @param  mixed  $value
+     * @param  array  $attributes
+     * @return mixed
+     */
+    public function get($model, string $key, $value, array $attributes);
+
+    /**
+     * Transform the attribute to its underlying model values.
+     *
+     * @param  \Illuminate\Database\Eloquent\Model  $model
+     * @param  string  $key
+     * @param  mixed  $value
+     * @param  array  $attributes
+     * @return array
+     */
+    public function set($model, string $key, $value, array $attributes);
+}
diff --git a/src/Illuminate/Contracts/Database/Eloquent/CastsInboundAttributes.php b/src/Illuminate/Contracts/Database/Eloquent/CastsInboundAttributes.php
new file mode 100644
index 000000000000..b9e3f922e689
--- /dev/null
+++ b/src/Illuminate/Contracts/Database/Eloquent/CastsInboundAttributes.php
@@ -0,0 +1,17 @@
+<?php
+
+namespace Illuminate\Contracts\Database\Eloquent;
+
+interface CastsInboundAttributes
+{
+    /**
+     * Transform the attribute to its underlying model values.
+     *
+     * @param  \Illuminate\Database\Eloquent\Model  $model
+     * @param  string  $key
+     * @param  mixed  $value
+     * @param  array  $attributes
+     * @return array
+     */
+    public function set($model, string $key, $value, array $attributes);
+}
diff --git a/src/Illuminate/Database/Eloquent/Concerns/HasAttributes.php b/src/Illuminate/Database/Eloquent/Concerns/HasAttributes.php
index 8563b4372dc6..a545f2d3f6c0 100644
--- a/src/Illuminate/Database/Eloquent/Concerns/HasAttributes.php
+++ b/src/Illuminate/Database/Eloquent/Concerns/HasAttributes.php
@@ -4,6 +4,7 @@
 
 use Carbon\CarbonInterface;
 use DateTimeInterface;
+use Illuminate\Contracts\Database\Eloquent\CastsInboundAttributes;
 use Illuminate\Contracts\Support\Arrayable;
 use Illuminate\Database\Eloquent\JsonEncodingException;
 use Illuminate\Database\Eloquent\Relations\Relation;
@@ -44,6 +45,38 @@ trait HasAttributes
      */
     protected $casts = [];
 
+    /**
+     * The attributes that have been cast using custom classes.
+     *
+     * @var array
+     */
+    protected $classCastCache = [];
+
+    /**
+     * The built-in, primitive cast types supported by Eloquent.
+     *
+     * @var array
+     */
+    protected static $primitiveCastTypes = [
+        'array',
+        'bool',
+        'boolean',
+        'collection',
+        'custom_datetime',
+        'date',
+        'datetime',
+        'decimal',
+        'double',
+        'float',
+        'int',
+        'integer',
+        'json',
+        'object',
+        'real',
+        'string',
+        'timestamp',
+    ];
+
     /**
      * The attributes that should be mutated to dates.
      *
@@ -173,7 +206,9 @@ protected function addMutatedAttributesToArray(array $attributes, array $mutated
     protected function addCastAttributesToArray(array $attributes, array $mutatedAttributes)
     {
         foreach ($this->getCasts() as $key => $value) {
-            if (! array_key_exists($key, $attributes) || in_array($key, $mutatedAttributes)) {
+            if (! array_key_exists($key, $attributes) ||
+                in_array($key, $mutatedAttributes) ||
+                $this->isClassCastable($key)) {
                 continue;
             }
 
@@ -211,7 +246,7 @@ protected function addCastAttributesToArray(array $attributes, array $mutatedAtt
      */
     protected function getArrayableAttributes()
     {
-        return $this->getArrayableItems($this->attributes);
+        return $this->getArrayableItems($this->getAttributes());
     }
 
     /**
@@ -318,8 +353,9 @@ public function getAttribute($key)
         // If the attribute exists in the attribute array or has a "get" mutator we will
         // get the attribute's value. Otherwise, we will proceed as if the developers
         // are asking for a relationship's value. This covers both types of values.
-        if (array_key_exists($key, $this->attributes) ||
-            $this->hasGetMutator($key)) {
+        if (array_key_exists($key, $this->getAttributes()) ||
+            $this->hasGetMutator($key) ||
+            $this->isClassCastable($key)) {
             return $this->getAttributeValue($key);
         }
 
@@ -352,7 +388,7 @@ public function getAttributeValue($key)
      */
     protected function getAttributeFromArray($key)
     {
-        return $this->attributes[$key] ?? null;
+        return $this->getAttributes()[$key] ?? null;
     }
 
     /**
@@ -439,7 +475,9 @@ protected function mutateAttribute($key, $value)
      */
     protected function mutateAttributeForArray($key, $value)
     {
-        $value = $this->mutateAttribute($key, $value);
+        $value = $this->isClassCastable($key)
+                    ? $this->getClassCastableAttributeValue($key)
+                    : $this->mutateAttribute($key, $value);
 
         return $value instanceof Arrayable ? $value->toArray() : $value;
     }
@@ -453,11 +491,13 @@ protected function mutateAttributeForArray($key, $value)
      */
     protected function castAttribute($key, $value)
     {
-        if (is_null($value)) {
+        $castType = $this->getCastType($key);
+
+        if (is_null($value) && in_array($castType, static::$primitiveCastTypes)) {
             return $value;
         }
 
-        switch ($this->getCastType($key)) {
+        switch ($castType) {
             case 'int':
             case 'integer':
                 return (int) $value;
@@ -486,8 +526,31 @@ protected function castAttribute($key, $value)
                 return $this->asDateTime($value);
             case 'timestamp':
                 return $this->asTimestamp($value);
-            default:
-                return $value;
+        }
+
+        if ($this->isClassCastable($key)) {
+            return $this->getClassCastableAttributeValue($key);
+        }
+
+        return $value;
+    }
+
+    /**
+     * Cast the given attribute using a custom cast class.
+     *
+     * @param  string  $key
+     * @return mixed
+     */
+    protected function getClassCastableAttributeValue($key)
+    {
+        if (isset($this->classCastCache[$key])) {
+            return $this->classCastCache[$key];
+        } else {
+            $caster = $this->resolveCasterClass($key);
+
+            return $this->classCastCache[$key] = $caster instanceof CastsInboundAttributes
+                ? $this->attributes[$key]
+                : $caster->get($this, $key, $this->attributes[$key] ?? null, $this->attributes);
         }
     }
 
@@ -556,6 +619,12 @@ public function setAttribute($key, $value)
             $value = $this->fromDateTime($value);
         }
 
+        if ($this->isClassCastable($key)) {
+            $this->setClassCastableAttribute($key, $value);
+
+            return $this;
+        }
+
         if ($this->isJsonCastable($key) && ! is_null($value)) {
             $value = $this->castAttributeAsJson($key, $value);
         }
@@ -625,6 +694,35 @@ public function fillJsonAttribute($key, $value)
         return $this;
     }
 
+    /**
+     * Set the value of a class castable attribute.
+     *
+     * @param  string  $key
+     * @param  mixed  $value
+     * @return void
+     */
+    protected function setClassCastableAttribute($key, $value)
+    {
+        if (is_null($value)) {
+            $this->attributes = array_merge($this->attributes, array_map(
+                function () {
+                },
+                $this->normalizeCastClassResponse($key, $this->resolveCasterClass($key)->set(
+                    $this, $key, $this->{$key}, $this->attributes
+                ))
+            ));
+        } else {
+            $this->attributes = array_merge(
+                $this->attributes,
+                $this->normalizeCastClassResponse($key, $this->resolveCasterClass($key)->set(
+                    $this, $key, $value, $this->attributes
+                ))
+            );
+        }
+
+        unset($this->classCastCache[$key]);
+    }
+
     /**
      * Get an array attribute with the given key and value set.
      *
@@ -926,6 +1024,67 @@ protected function isJsonCastable($key)
         return $this->hasCast($key, ['array', 'json', 'object', 'collection']);
     }
 
+    /**
+     * Determine if the given key is cast using a custom class.
+     *
+     * @param  string  $key
+     * @return bool
+     */
+    protected function isClassCastable($key)
+    {
+        return array_key_exists($key, $this->getCasts()) &&
+                class_exists($class = $this->getCasts()[$key]) &&
+                ! in_array($class, static::$primitiveCastTypes);
+    }
+
+    /**
+     * Resolve the custom caster class for a given key.
+     *
+     * @param  string  $key
+     * @return mixed
+     */
+    protected function resolveCasterClass($key)
+    {
+        if (strpos($castType = $this->getCasts()[$key], ':') === false) {
+            return new $castType;
+        }
+
+        $segments = explode(':', $castType, 2);
+
+        return new $segments[0](...explode(',', $segments[1]));
+    }
+
+    /**
+     * Merge the cast class attributes back into the model.
+     *
+     * @return void
+     */
+    protected function mergeAttributesFromClassCasts()
+    {
+        foreach ($this->classCastCache as $key => $value) {
+            $caster = $this->resolveCasterClass($key);
+
+            $this->attributes = array_merge(
+                $this->attributes,
+                $caster instanceof CastsInboundAttributes
+                       ? [$key => $value]
+                       : $this->normalizeCastClassResponse($key, $caster->set($this, $key, $value, $this->attributes))
+            );
+        }
+    }
+
+    /**
+     * Normalize the response from a custom class caster.
+     *
+     * @param  string  $key
+     * @param  mixed  $value
+     * @return array
+     */
+    protected function normalizeCastClassResponse($key, $value)
+    {
+        return is_array($value) ? $value : [$key => $value];
+    }
+
     /**
      * Get all of the current attributes on the model.
      *
@@ -933,6 +1092,8 @@ protected function isJsonCastable($key)
      */
     public function getAttributes()
     {
+        $this->mergeAttributesFromClassCasts();
+
         return $this->attributes;
     }
 
@@ -951,6 +1112,8 @@ public function setRawAttributes(array $attributes, $sync = false)
             $this->syncOriginal();
         }
 
+        $this->classCastCache = [];
+
         return $this;
     }
 
@@ -998,7 +1161,7 @@ public function only($attributes)
      */
     public function syncOriginal()
     {
-        $this->original = $this->attributes;
+        $this->original = $this->getAttributes();
 
         return $this;
     }
@@ -1024,8 +1187,10 @@ public function syncOriginalAttributes($attributes)
     {
         $attributes = is_array($attributes) ? $attributes : func_get_args();
 
+        $modelAttributes = $this->getAttributes();
+
         foreach ($attributes as $attribute) {
-            $this->original[$attribute] = $this->attributes[$attribute];
+            $this->original[$attribute] = $modelAttributes[$attribute];
         }
 
         return $this;
diff --git a/src/Illuminate/Database/Eloquent/Model.php b/src/Illuminate/Database/Eloquent/Model.php
index eb8a4e692c8c..0e1f50103265 100644
--- a/src/Illuminate/Database/Eloquent/Model.php
+++ b/src/Illuminate/Database/Eloquent/Model.php
@@ -665,6 +665,8 @@ public function push()
      */
     public function save(array $options = [])
     {
+        $this->mergeAttributesFromClassCasts();
+
         $query = $this->newModelQuery();
 
         // If the "saving" event returns false we'll bail out of the save and return
@@ -905,6 +907,8 @@ public static function destroy($ids)
      */
     public function delete()
     {
+        $this->mergeAttributesFromClassCasts();
+
         if (is_null($this->getKeyName())) {
             throw new Exception('No primary key defined on model.');
         }
@@ -1194,7 +1198,7 @@ public function replicate(array $except = null)
         ];
 
         $attributes = Arr::except(
-            $this->attributes, $except ? array_unique(array_merge($except, $defaults)) : $defaults
+            $this->getAttributes(), $except ? array_unique(array_merge($except, $defaults)) : $defaults
         );
 
         return tap(new static, function ($instance) use ($attributes) {
@@ -1676,6 +1680,20 @@ public function __toString()
         return $this->toJson();
     }
 
+    /**
+     * Prepare the object for serialization.
+     *
+     * @return array
+     */
+    public function __sleep()
+    {
+        $this->mergeAttributesFromClassCasts();
+
+        $this->classCastCache = [];
+
+        return array_keys(get_object_vars($this));
+    }
+
     /**
      * When a model is being unserialized, check if it needs to be booted.
      *
diff --git a/tests/Integration/Database/DatabaseEloquentModelCustomCastingTest.php b/tests/Integration/Database/DatabaseEloquentModelCustomCastingTest.php
new file mode 100644
index 000000000000..f5594ee62bcd
--- /dev/null
+++ b/tests/Integration/Database/DatabaseEloquentModelCustomCastingTest.php
@@ -0,0 +1,183 @@
+<?php
+
+namespace Illuminate\Tests\Integration\Database;
+
+use Illuminate\Contracts\Database\Eloquent\CastsAttributes;
+use Illuminate\Contracts\Database\Eloquent\CastsInboundAttributes;
+use Illuminate\Database\Eloquent\Model;
+
+/**
+ * @group integration
+ */
+class DatabaseEloquentModelCustomCastingTest extends DatabaseTestCase
+{
+    public function testBasicCustomCasting()
+    {
+        $model = new TestEloquentModelWithCustomCast;
+        $model->reversed = 'taylor';
+
+        $this->assertEquals('taylor', $model->reversed);
+        $this->assertEquals('rolyat', $model->getAttributes()['reversed']);
+        $this->assertEquals('rolyat', $model->toArray()['reversed']);
+
+        $unserializedModel = unserialize(serialize($model));
+
+        $this->assertEquals('taylor', $unserializedModel->reversed);
+        $this->assertEquals('rolyat', $unserializedModel->getAttributes()['reversed']);
+        $this->assertEquals('rolyat', $unserializedModel->toArray()['reversed']);
+
+        $model->setRawAttributes([
+            'address_line_one' => '110 Kingsbrook St.',
+            'address_line_two' => 'My House',
+        ]);
+
+        $this->assertEquals('110 Kingsbrook St.', $model->address->lineOne);
+        $this->assertEquals('My House', $model->address->lineTwo);
+
+        $this->assertEquals('110 Kingsbrook St.', $model->toArray()['address_line_one']);
+        $this->assertEquals('My House', $model->toArray()['address_line_two']);
+
+        $model->address->lineOne = '117 Spencer St.';
+
+        $this->assertFalse(isset($model->toArray()['address']));
+        $this->assertEquals('117 Spencer St.', $model->toArray()['address_line_one']);
+        $this->assertEquals('My House', $model->toArray()['address_line_two']);
+
+        $this->assertEquals('117 Spencer St.', json_decode($model->toJson(), true)['address_line_one']);
+        $this->assertEquals('My House', json_decode($model->toJson(), true)['address_line_two']);
+
+        $model->address = null;
+
+        $this->assertNull($model->toArray()['address_line_one']);
+        $this->assertNull($model->toArray()['address_line_two']);
+
+        $model->options = ['foo' => 'bar'];
+        $this->assertEquals(['foo' => 'bar'], $model->options);
+        $this->assertEquals(['foo' => 'bar'], $model->options);
+        $model->options = ['foo' => 'bar'];
+        $model->options = ['foo' => 'bar'];
+        $this->assertEquals(['foo' => 'bar'], $model->options);
+        $this->assertEquals(['foo' => 'bar'], $model->options);
+
+        $this->assertEquals(json_encode(['foo' => 'bar']), $model->getAttributes()['options']);
+    }
+
+    public function testOneWayCasting()
+    {
+        // CastsInboundAttributes is used for casting that is unidirectional... only use case I can think of is one-way hashing...
+        $model = new TestEloquentModelWithCustomCast;
+
+        $model->password = 'secret';
+
+        $this->assertEquals(hash('sha256', 'secret'), $model->password);
+        $this->assertEquals(hash('sha256', 'secret'), $model->getAttributes()['password']);
+        $this->assertEquals(hash('sha256', 'secret'), $model->getAttributes()['password']);
+        $this->assertEquals(hash('sha256', 'secret'), $model->password);
+
+        $model->password = 'secret2';
+
+        $this->assertEquals(hash('sha256', 'secret2'), $model->password);
+        $this->assertEquals(hash('sha256', 'secret2'), $model->getAttributes()['password']);
+        $this->assertEquals(hash('sha256', 'secret2'), $model->getAttributes()['password']);
+        $this->assertEquals(hash('sha256', 'secret2'), $model->password);
+    }
+
+    public function testSettingRawAttributesClearsTheCastCache()
+    {
+        $model = new TestEloquentModelWithCustomCast;
+
+        $model->setRawAttributes([
+            'address_line_one' => '110 Kingsbrook St.',
+            'address_line_two' => 'My House',
+        ]);
+
+        $this->assertEquals('110 Kingsbrook St.', $model->address->lineOne);
+
+        $model->setRawAttributes([
+            'address_line_one' => '117 Spencer St.',
+            'address_line_two' => 'My House',
+        ]);
+
+        $this->assertEquals('117 Spencer St.', $model->address->lineOne);
+    }
+}
+
+class TestEloquentModelWithCustomCast extends Model
+{
+    /**
+     * The attributes that should be cast to native types.
+     *
+     * @var array
+     */
+    protected $casts = [
+        'address' => AddressCaster::class,
+        'password' => HashCaster::class,
+        'other_password' => HashCaster::class.':md5',
+        'reversed' => ReverseCaster::class,
+        'options' => JsonCaster::class,
+    ];
+}
+
+class HashCaster implements CastsInboundAttributes
+{
+    public function __construct($algorithm = 'sha256')
+    {
+        $this->algorithm = $algorithm;
+    }
+
+    public function set($model, $key, $value, $attributes)
+    {
+        return [$key => hash($this->algorithm, $value)];
+    }
+}
+
+class ReverseCaster implements CastsAttributes
+{
+    public function get($model, $key, $value, $attributes)
+    {
+        return strrev($value);
+    }
+
+    public function set($model, $key, $value, $attributes)
+    {
+        return [$key => strrev($value)];
+    }
+}
+
+class AddressCaster implements CastsAttributes
+{
+    public function get($model, $key, $value, $attributes)
+    {
+        return new Address($attributes['address_line_one'], $attributes['address_line_two']);
+    }
+
+    public function set($model, $key, $value, $attributes)
+    {
+        return ['address_line_one' => $value->lineOne, 'address_line_two' => $value->lineTwo];
+    }
+}
+
+class JsonCaster implements CastsAttributes
+{
+    public function get($model, $key, $value, $attributes)
+    {
+        return json_decode($value, true);
+    }
+
+    public function set($model, $key, $value, $attributes)
+    {
+        return json_encode($value);
+    }
+}
+
+class Address
+{
+    public $lineOne;
+    public $lineTwo;
+
+    public function __construct($lineOne, $lineTwo)
+    {
+        $this->lineOne = $lineOne;
+        $this->lineTwo = $lineTwo;
+    }
+}