diff --git a/NEWS b/NEWS
index 5bb69bd52a4..150586fe470 100644
--- a/NEWS
+++ b/NEWS
@@ -3,6 +3,7 @@ PHP                                                                        NEWS
 ?? ??? 2016, PHP 7.1.0
 
 - Core:
+  . Added nullable types. (Levi, Dmitry)
   . Added DFA optimization framework based on e-SSA form. (Dmitry, Nikita)
   . Added specialized opcode handlers (e.g. ZEND_ADD_LONG_NO_OVERFLOW).
     (Dmitry)
diff --git a/Zend/tests/bug71428.1.phpt b/Zend/tests/bug71428.1.phpt
index fbf342380ff..e4d3a22f670 100644
--- a/Zend/tests/bug71428.1.phpt
+++ b/Zend/tests/bug71428.1.phpt
@@ -1,7 +1,5 @@
 --TEST--
 bug #71428.1: inheritance with null default values
---XFAIL--
-This is a BC break
 --FILE--
 <?php
 class A {
@@ -11,5 +9,5 @@ class B extends A {
     public function m(array $a = []) {}
 }
 --EXPECTF--
-Warning: Declaration of B::m(array $a = Array) should be compatible with A::m(array $a = NULL) in %sbug71428.1.php on line 7
+Warning: Declaration of B::m(array $a = Array) should be compatible with A::m(?array $a = NULL) in %sbug71428.1.php on line 7
 
diff --git a/Zend/tests/bug71428.3.phpt b/Zend/tests/bug71428.3.phpt
index 65d397052e4..558e87c56e2 100644
--- a/Zend/tests/bug71428.3.phpt
+++ b/Zend/tests/bug71428.3.phpt
@@ -1,7 +1,5 @@
 --TEST--
 bug #71428: Validation type inheritance with = NULL
---XFAIL--
-This is a BC break
 --FILE--
 <?php
 class A { }
@@ -9,5 +7,5 @@ class B           {  public function m(A $a = NULL, $n) { echo "B.m";} };
 class C extends B {  public function m(A $a       , $n) { echo "C.m";} };
 ?>
 --EXPECTF--
-Warning: Declaration of C::m(A $a, $n) should be compatible with B::m(A $a = NULL, $n) in %sbug71428.3.php on line 4
+Warning: Declaration of C::m(A $a, $n) should be compatible with B::m(?A $a, $n) in %sbug71428.3.php on line 4
 
diff --git a/Zend/tests/bug72119.phpt b/Zend/tests/bug72119.phpt
index b8f070a25af..064381ada05 100644
--- a/Zend/tests/bug72119.phpt
+++ b/Zend/tests/bug72119.phpt
@@ -14,5 +14,6 @@ class Hello implements Foo {
 }
 echo "OK\n";
 ?>
---EXPECT--
-OK
+--EXPECTF--
+Fatal error: Declaration of Hello::bar(array $baz = Array) must be compatible with Foo::bar(?array $baz = NULL) in %s on line %d
+
diff --git a/Zend/tests/nullable_types/array.phpt b/Zend/tests/nullable_types/array.phpt
new file mode 100644
index 00000000000..7b0a2ed4d5a
--- /dev/null
+++ b/Zend/tests/nullable_types/array.phpt
@@ -0,0 +1,17 @@
+--TEST--
+Explicitly nullable array type
+--FILE--
+<?php
+
+function _array_(?array $v): ?array {
+    return $v;
+}
+
+var_dump(_array_(null));
+var_dump(_array_([]));
+
+--EXPECT--
+NULL
+array(0) {
+}
+
diff --git a/Zend/tests/nullable_types/contravariant_nullable_param_succeeds.phpt b/Zend/tests/nullable_types/contravariant_nullable_param_succeeds.phpt
new file mode 100644
index 00000000000..f4d1e315fc8
--- /dev/null
+++ b/Zend/tests/nullable_types/contravariant_nullable_param_succeeds.phpt
@@ -0,0 +1,19 @@
+--TEST--
+Subtype can add nullability to a parameter (contravariance)
+
+--FILE--
+<?php
+
+interface A {
+    function method(int $p);
+}
+
+class B implements A {
+    function method(?int $p) { }
+}
+
+$b = new B();
+$b->method(null);
+
+--EXPECT--
+
diff --git a/Zend/tests/nullable_types/contravariant_nullable_return_fails.phpt b/Zend/tests/nullable_types/contravariant_nullable_return_fails.phpt
new file mode 100644
index 00000000000..c9be479ead3
--- /dev/null
+++ b/Zend/tests/nullable_types/contravariant_nullable_return_fails.phpt
@@ -0,0 +1,17 @@
+--TEST--
+Return type cannot add nullability (contravariance)
+
+--FILE--
+<?php
+
+interface A {
+    function method(): int;
+}
+
+interface B extends A {
+    function method(): ?int;
+}
+
+--EXPECTF--
+Fatal error: Declaration of B::method(): ?int must be compatible with A::method(): int in %s on line %d
+
diff --git a/Zend/tests/nullable_types/covariant_nullable_param_fails.phpt b/Zend/tests/nullable_types/covariant_nullable_param_fails.phpt
new file mode 100644
index 00000000000..65b2858e6b9
--- /dev/null
+++ b/Zend/tests/nullable_types/covariant_nullable_param_fails.phpt
@@ -0,0 +1,17 @@
+--TEST--
+Subtype cannot remove nullable parameter (covariance)
+
+--FILE--
+<?php
+
+interface A {
+    function method(?int $p);
+}
+
+class B implements A {
+    function method(int $p) { }
+}
+
+--EXPECTF--
+Fatal error: Declaration of B::method(int $p) must be compatible with A::method(?int $p) in %s on line %d
+
diff --git a/Zend/tests/nullable_types/covariant_nullable_return_succeds.phpt b/Zend/tests/nullable_types/covariant_nullable_return_succeds.phpt
new file mode 100644
index 00000000000..5776f9b99d4
--- /dev/null
+++ b/Zend/tests/nullable_types/covariant_nullable_return_succeds.phpt
@@ -0,0 +1,16 @@
+--TEST--
+Nullable covariant return types
+
+--FILE--
+<?php
+
+interface A {
+    function method(): ?int;
+}
+
+interface B extends A {
+    function method(): int;
+}
+
+--EXPECT--
+
diff --git a/Zend/tests/nullable_types/float.phpt b/Zend/tests/nullable_types/float.phpt
new file mode 100644
index 00000000000..8e44524cf01
--- /dev/null
+++ b/Zend/tests/nullable_types/float.phpt
@@ -0,0 +1,16 @@
+--TEST--
+Explicitly nullable float type
+--FILE--
+<?php
+
+function _float_(?float $v): ?float {
+    return $v;
+}
+
+var_dump(_float_(null));
+var_dump(_float_(1.3));
+
+--EXPECT--
+NULL
+float(1.3)
+
diff --git a/Zend/tests/nullable_types/int.phpt b/Zend/tests/nullable_types/int.phpt
new file mode 100644
index 00000000000..ec75132edbe
--- /dev/null
+++ b/Zend/tests/nullable_types/int.phpt
@@ -0,0 +1,16 @@
+--TEST--
+Explicitly nullable int type
+--FILE--
+<?php
+
+function _int_(?int $v): ?int {
+    return $v;
+}
+
+var_dump(_int_(null));
+var_dump(_int_(1));
+
+--EXPECT--
+NULL
+int(1)
+
diff --git a/Zend/tests/nullable_types/invariant_param_and_return_succeeds.phpt b/Zend/tests/nullable_types/invariant_param_and_return_succeeds.phpt
new file mode 100644
index 00000000000..0542e52c0f7
--- /dev/null
+++ b/Zend/tests/nullable_types/invariant_param_and_return_succeeds.phpt
@@ -0,0 +1,24 @@
+--TEST--
+Invariant parameter and return types work with nullable types
+
+--FILE--
+<?php
+
+interface A {
+    function method(?int $i): ?int;
+}
+
+class B implements A {
+    function method(?int $i): ?int {
+        return $i;
+    }
+}
+
+$b = new B();
+var_dump($b->method(null));
+var_dump($b->method(1));
+
+--EXPECT--
+NULL
+int(1)
+
diff --git a/Zend/tests/nullable_types/nullable_type_parameters_do_not_have_default_value.phpt b/Zend/tests/nullable_types/nullable_type_parameters_do_not_have_default_value.phpt
new file mode 100644
index 00000000000..13b25e0daca
--- /dev/null
+++ b/Zend/tests/nullable_types/nullable_type_parameters_do_not_have_default_value.phpt
@@ -0,0 +1,17 @@
+--TEST--
+Explicit nullable types do not imply a default value
+
+--FILE--
+<?php
+
+function f(?callable $p) {}
+
+f();
+
+--EXPECTF--
+Fatal error: Uncaught TypeError: Argument 1 passed to f() must be callable, none given, called in %s on line %d and defined in %s:%d
+Stack trace:
+#%d %s
+#%d %s
+  thrown in %s on line %d
+
diff --git a/Zend/tests/nullable_types/string.phpt b/Zend/tests/nullable_types/string.phpt
new file mode 100644
index 00000000000..ffc6591b6bb
--- /dev/null
+++ b/Zend/tests/nullable_types/string.phpt
@@ -0,0 +1,16 @@
+--TEST--
+Explicitly nullable string type
+--FILE--
+<?php
+
+function _string_(?string $v): ?string {
+    return $v;
+}
+
+var_dump(_string_(null));
+var_dump(_string_("php"));
+
+--EXPECT--
+NULL
+string(3) "php"
+
diff --git a/Zend/tests/return_types/030.phpt b/Zend/tests/return_types/030.phpt
new file mode 100644
index 00000000000..d1ceac83299
--- /dev/null
+++ b/Zend/tests/return_types/030.phpt
@@ -0,0 +1,23 @@
+--TEST--
+Nullable return value 
+--FILE--
+<?php
+function foo($x) : ?array {
+	return $x;
+}
+
+foo([]);
+echo "ok\n";
+foo(null);
+echo "ok\n";
+foo(0);
+?>
+--EXPECTF--
+ok
+ok
+
+Fatal error: Uncaught TypeError: Return value of foo() must be of the type array, integer returned in %s030.php:3
+Stack trace:
+#0 %s030.php(10): foo(0)
+#1 {main}
+  thrown in %s030.php on line 3
diff --git a/Zend/tests/return_types/031.phpt b/Zend/tests/return_types/031.phpt
new file mode 100644
index 00000000000..91ee2f8ce4b
--- /dev/null
+++ b/Zend/tests/return_types/031.phpt
@@ -0,0 +1,14 @@
+--TEST--
+Nullable return type inheritance rules (non-nullable and nullable)
+--FILE--
+<?php
+class A {
+	function foo(): int {}
+}
+class B extends A {
+	function foo(): ?int {}
+}
+?>
+DONE
+--EXPECTF--
+Fatal error: Declaration of B::foo(): ?int must be compatible with A::foo(): int in %s031.php on line 7
\ No newline at end of file
diff --git a/Zend/tests/return_types/032.phpt b/Zend/tests/return_types/032.phpt
new file mode 100644
index 00000000000..00790b5d608
--- /dev/null
+++ b/Zend/tests/return_types/032.phpt
@@ -0,0 +1,14 @@
+--TEST--
+Nullable return type inheritance rules (nullable and non-nullable)
+--FILE--
+<?php
+class A {
+	function foo(): ?int {}
+}
+class B extends A {
+	function foo(): int {}
+}
+?>
+DONE
+--EXPECT--
+DONE
diff --git a/Zend/tests/variadic/adding_additional_optional_parameter_error.phpt b/Zend/tests/variadic/adding_additional_optional_parameter_error.phpt
index da96264609d..4c6f36f10b5 100644
--- a/Zend/tests/variadic/adding_additional_optional_parameter_error.phpt
+++ b/Zend/tests/variadic/adding_additional_optional_parameter_error.phpt
@@ -13,4 +13,4 @@ class MySQL implements DB {
 
 ?>
 --EXPECTF--
-Fatal error: Declaration of MySQL::query($query, int $extraParam = NULL, string ...$params) must be compatible with DB::query($query, string ...$params) in %s on line %d
+Fatal error: Declaration of MySQL::query($query, ?int $extraParam = NULL, string ...$params) must be compatible with DB::query($query, string ...$params) in %s on line %d
diff --git a/Zend/zend_compile.c b/Zend/zend_compile.c
index e401ce24303..0994681c209 100644
--- a/Zend/zend_compile.c
+++ b/Zend/zend_compile.c
@@ -4889,7 +4889,7 @@ static void zend_compile_typename(zend_ast *ast, zend_arg_info *arg_info) /* {{{
 		zend_uchar type = zend_lookup_builtin_type_by_name(class_name);
 
 		if (type != 0) {
-			if (ast->attr != ZEND_NAME_NOT_FQ) {
+			if ((ast->attr & ZEND_NAME_NOT_FQ) != ZEND_NAME_NOT_FQ) {
 				zend_error_noreturn(E_COMPILE_ERROR,
 					"Scalar type declaration '%s' must be unqualified",
 					ZSTR_VAL(zend_string_tolower(class_name)));
@@ -4929,6 +4929,11 @@ void zend_compile_params(zend_ast *ast, zend_ast *return_type_ast) /* {{{ */
 		arg_infos->allow_null = 0;
 		arg_infos->class_name = NULL;
 
+		if (return_type_ast->attr & ZEND_TYPE_NULLABLE) {
+			arg_infos->allow_null = 1;
+			return_type_ast->attr &= ~ZEND_TYPE_NULLABLE;
+		}
+
 		zend_compile_typename(return_type_ast, arg_infos);
 
 		arg_infos++;
@@ -5017,9 +5022,10 @@ void zend_compile_params(zend_ast *ast, zend_ast *return_type_ast) /* {{{ */
 				&& (Z_TYPE(default_node.u.constant) == IS_NULL
 					|| (Z_TYPE(default_node.u.constant) == IS_CONSTANT
 						&& strcasecmp(Z_STRVAL(default_node.u.constant), "NULL") == 0));
+			zend_bool is_explicitly_nullable = (type_ast->attr & ZEND_TYPE_NULLABLE) == ZEND_TYPE_NULLABLE;
 
 			op_array->fn_flags |= ZEND_ACC_HAS_TYPE_HINTS;
-			arg_info->allow_null = has_null_default;
+			arg_info->allow_null = has_null_default || is_explicitly_nullable;
 
 			zend_compile_typename(type_ast, arg_info);
 
diff --git a/Zend/zend_compile.h b/Zend/zend_compile.h
index 344293273a2..0de475da11d 100644
--- a/Zend/zend_compile.h
+++ b/Zend/zend_compile.h
@@ -839,6 +839,8 @@ ZEND_API void zend_assert_valid_class_name(const zend_string *const_name);
 #define ZEND_NAME_NOT_FQ   1
 #define ZEND_NAME_RELATIVE 2
 
+#define ZEND_TYPE_NULLABLE (1<<8)
+
 /* var status for backpatching */
 #define BP_VAR_R			0
 #define BP_VAR_W			1
diff --git a/Zend/zend_inheritance.c b/Zend/zend_inheritance.c
index edb2bbe5afa..44abfb6ffba 100644
--- a/Zend/zend_inheritance.c
+++ b/Zend/zend_inheritance.c
@@ -319,13 +319,11 @@ static zend_bool zend_do_perform_implementation_check(const zend_function *fe, c
 			return 0;
 		}
 
-#if 0
 		// This introduces BC break described at https://bugs.php.net/bug.php?id=72119
 		if (proto_arg_info->type_hint && proto_arg_info->allow_null && !fe_arg_info->allow_null) {
 			/* incompatible nullability */
 			return 0;
 		}
-#endif
 
 		/* by-ref constraints on arguments are invariant */
 		if (fe_arg_info->pass_by_reference != proto_arg_info->pass_by_reference) {
@@ -344,6 +342,10 @@ static zend_bool zend_do_perform_implementation_check(const zend_function *fe, c
 		if (!zend_do_perform_type_hint_check(fe, fe->common.arg_info - 1, proto, proto->common.arg_info - 1)) {
 			return 0;
 		}
+
+		if (fe->common.arg_info[-1].allow_null && !proto->common.arg_info[-1].allow_null) {
+			return 0;
+		}
 	}
 	return 1;
 }
@@ -351,6 +353,11 @@ static zend_bool zend_do_perform_implementation_check(const zend_function *fe, c
 
 static ZEND_COLD void zend_append_type_hint(smart_str *str, const zend_function *fptr, zend_arg_info *arg_info, int return_hint) /* {{{ */
 {
+
+	if (arg_info->type_hint != IS_UNDEF && arg_info->allow_null) {
+		smart_str_appendc(str, '?');
+	}
+
 	if (arg_info->class_name) {
 		const char *class_name;
 		size_t class_name_len;
@@ -491,8 +498,6 @@ static ZEND_COLD zend_string *zend_get_function_declaration(const zend_function
 				} else {
 					smart_str_appends(&str, "NULL");
 				}
-			} else if (arg_info->type_hint && arg_info->allow_null) {
-				smart_str_appends(&str, " = NULL");
 			}
 
 			if (++i < num_args) {
@@ -590,7 +595,8 @@ static void do_inheritance_check_on_method(zend_function *child, zend_function *
 			error_verb = "must";
 		} else if ((parent->common.fn_flags & ZEND_ACC_HAS_RETURN_TYPE) &&
                    (!(child->common.fn_flags & ZEND_ACC_HAS_RETURN_TYPE) ||
-		            !zend_do_perform_type_hint_check(child, child->common.arg_info - 1, parent, parent->common.arg_info - 1))) {
+		            !zend_do_perform_type_hint_check(child, child->common.arg_info - 1, parent, parent->common.arg_info - 1) ||
+		            (child->common.arg_info[-1].allow_null && !parent->common.arg_info[-1].allow_null))) {
 			error_level = E_COMPILE_ERROR;
 			error_verb = "must";
 		} else {
diff --git a/Zend/zend_language_parser.y b/Zend/zend_language_parser.y
index 5f233d6a3b8..44c5cfb12b5 100644
--- a/Zend/zend_language_parser.y
+++ b/Zend/zend_language_parser.y
@@ -251,7 +251,7 @@ static YYSIZE_T zend_yytnamerr(char*, const char*);
 %type <ast> ctor_arguments alt_if_stmt_without_else trait_adaptation_list lexical_vars
 %type <ast> lexical_var_list encaps_list
 %type <ast> array_pair non_empty_array_pair_list array_pair_list
-%type <ast> isset_variable type return_type
+%type <ast> isset_variable type return_type type_expr
 %type <ast> identifier
 
 %type <num> returns_ref function is_reference is_variadic variable_modifiers
@@ -644,7 +644,12 @@ parameter:
 
 optional_type:
 		/* empty */	{ $$ = NULL; }
-	|	type		{ $$ = $1; }
+	|	type_expr	{ $$ = $1; }
+;
+
+type_expr:
+		type		{ $$ = $1; }
+	|	'?' type	{ $$ = $2; $$->attr |= ZEND_TYPE_NULLABLE; }
 ;
 
 type:
@@ -655,7 +660,7 @@ type:
 
 return_type:
 		/* empty */	{ $$ = NULL; }
-	|	':' type	{ $$ = $2; }
+	|	':' type_expr	{ $$ = $2; }
 ;
 
 argument_list: