diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index ff71c521b55..a90006431d2 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -16,7 +16,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        php-versions: ['7.3', '7.4']
+        php-versions: ['7.3', '7.4', '8.0']
         dependencies: ['highest']
         composer-arguments: [''] # to run --ignore-platform-reqs in experimental builds
         static-analysis: ['no']
@@ -27,8 +27,8 @@ jobs:
           #  experimental: false
           #  dependencies: 'highest'
 
-          # Experimental build for PHP 8
-          #- php-versions: '8.0'
+          # Experimental build for PHP nightly
+          #- php-versions: 'nightly'
           #  composer-arguments: '--ignore-platform-reqs'
           #  static-analysis: 'no'
           #  experimental: true
diff --git a/Neos.ContentRepository/Classes/Domain/Model/NodeData.php b/Neos.ContentRepository/Classes/Domain/Model/NodeData.php
index 38159d86e09..631e03f1c89 100644
--- a/Neos.ContentRepository/Classes/Domain/Model/NodeData.php
+++ b/Neos.ContentRepository/Classes/Domain/Model/NodeData.php
@@ -558,7 +558,7 @@ function ($childNodeData) {
      * @param array $dimensions
      * @return integer The number of child nodes
      */
-    public function getNumberOfChildNodes($nodeTypeFilter = null, Workspace $workspace, array $dimensions)
+    public function getNumberOfChildNodes($nodeTypeFilter, Workspace $workspace, array $dimensions)
     {
         return $this->nodeDataRepository->countByParentAndNodeType($this->path, $nodeTypeFilter, $workspace, $dimensions);
     }
diff --git a/Neos.ContentRepository/Tests/Functional/Domain/NodesTest.php b/Neos.ContentRepository/Tests/Functional/Domain/NodesTest.php
index b3a35c39a4c..d34d6f52fe8 100644
--- a/Neos.ContentRepository/Tests/Functional/Domain/NodesTest.php
+++ b/Neos.ContentRepository/Tests/Functional/Domain/NodesTest.php
@@ -1098,9 +1098,9 @@ public function nodesCanBeCopiedBefore()
         $childNodes = $rootNode->getChildNodes();
         $names = new \stdClass();
         $names->names = [];
-        array_walk($childNodes, function ($value, $key, &$names) {
+        array_walk($childNodes, function ($value, $key) use (&$names) {
             $names->names[] = $value->getName();
-        }, $names);
+        });
         self::assertSame(['fluss', 'baz', 'flux'], $names->names);
     }
 
@@ -1119,9 +1119,9 @@ public function nodesCanBeCopiedAfter()
         $childNodes = $rootNode->getChildNodes();
         $names = new \stdClass();
         $names->names = [];
-        array_walk($childNodes, function ($value, $key, &$names) {
+        array_walk($childNodes, function ($value, $key) use (&$names) {
             $names->names[] = $value->getName();
-        }, $names);
+        });
         self::assertSame(['baz', 'fluss', 'flux'], $names->names);
     }
 
@@ -1174,9 +1174,9 @@ public function nodesAreCopiedBeforeRecursively()
 
         $names = new \stdClass();
         $names->names = [];
-        array_walk($copiedChildNodes, function ($value, $key, &$names) {
+        array_walk($copiedChildNodes, function ($value, $key) use (&$names) {
             $names->names[] = $value->getName();
-        }, $names);
+        });
         self::assertSame(['capacitor', 'second', 'third'], $names->names);
     }
 
@@ -1197,9 +1197,9 @@ public function nodesAreCopiedAfterRecursively()
 
         $names = new \stdClass();
         $names->names = [];
-        array_walk($copiedChildNodes, function ($value, $key, &$names) {
+        array_walk($copiedChildNodes, function ($value, $key) use (&$names) {
             $names->names[] = $value->getName();
-        }, $names);
+        });
         self::assertSame(['capacitor', 'second', 'third'], $names->names);
     }
 
diff --git a/Neos.ContentRepository/Tests/Unit/Domain/Service/NodeServiceTest.php b/Neos.ContentRepository/Tests/Unit/Domain/Service/NodeServiceTest.php
index c62308a7026..fae6de971ac 100644
--- a/Neos.ContentRepository/Tests/Unit/Domain/Service/NodeServiceTest.php
+++ b/Neos.ContentRepository/Tests/Unit/Domain/Service/NodeServiceTest.php
@@ -17,6 +17,7 @@
 use Neos\ContentRepository\Domain\Model\NodeType;
 use Neos\ContentRepository\Domain\Service\NodeService;
 use Neos\ContentRepository\Domain\Service\NodeTypeManager;
+use Neos\Flow\Utility\Algorithms;
 
 /**
  * Testcase for the NodeService
@@ -196,7 +197,7 @@ public function createChildNodesTryToCreateAllConfiguredChildNodes()
     {
         $nodeService = $this->createNodeService();
 
-        $mockNode = $this->getMockBuilder(Node::class)->disableOriginalConstructor()->getMock();
+        $mockNode = $this->getMockBuilder(Node::class)->disableOriginalConstructor()->onlyMethods(['getNodeType', 'createNode', 'getIdentifier'])->getMock();
 
         $mockNodeType = $this->mockNodeType('Neos.ContentRepository.Testing:Content');
         $firstChildNodeType = $this->mockNodeType('Neos.ContentRepository.Testing:Content');
@@ -209,6 +210,8 @@ public function createChildNodesTryToCreateAllConfiguredChildNodes()
                 'second-child-node-name' => $secondChildNodeType
             ]));
 
+        $mockNode->method('getIdentifier')->willReturn(Algorithms::generateUUID());
+
         $mockNode->expects(self::once())
             ->method('getNodeType')
             ->will(self::returnValue($mockNodeType));
diff --git a/Neos.ContentRepository/composer.json b/Neos.ContentRepository/composer.json
index c1bd62666b4..134bfd5e41c 100644
--- a/Neos.ContentRepository/composer.json
+++ b/Neos.ContentRepository/composer.json
@@ -6,7 +6,7 @@
         "GPL-3.0-or-later"
     ],
     "require": {
-        "php": "^7.3",
+        "php": "^7.3 || ^8.0",
         "neos/flow": "*",
         "neos/cache": "*",
         "neos/eel": "*",
@@ -126,4 +126,4 @@
             "Neos.Flow-20201109224100"
         ]
     }
-}
\ No newline at end of file
+}
diff --git a/Neos.Diff/composer.json b/Neos.Diff/composer.json
index 0da337d1324..880cd4c93a9 100644
--- a/Neos.Diff/composer.json
+++ b/Neos.Diff/composer.json
@@ -4,7 +4,7 @@
   "license": "BSD-3-Clause",
   "description": "This is a comprehensive library for generating differences between two strings or arrays",
   "require": {
-    "php": "^7.3"
+    "php": "^7.3 || ^8.0"
   },
   "autoload": {
     "psr-4": {
diff --git a/Neos.Fusion/Classes/Core/Cache/ContentCache.php b/Neos.Fusion/Classes/Core/Cache/ContentCache.php
index cc4e3d1ba89..7d494431422 100644
--- a/Neos.Fusion/Classes/Core/Cache/ContentCache.php
+++ b/Neos.Fusion/Classes/Core/Cache/ContentCache.php
@@ -157,7 +157,7 @@ public function createUncachedSegment($content, $fusionPath, array $contextVaria
      * @param string $cacheDiscriminator The evaluated cache discriminator value
      * @return string The original content, but with additional markers added
      */
-    public function createDynamicCachedSegment($content, $fusionPath, array $contextVariables, array $cacheIdentifierValues, array $tags = [], $lifetime = null, $cacheDiscriminator)
+    public function createDynamicCachedSegment($content, $fusionPath, array $contextVariables, array $cacheIdentifierValues, array $tags, $lifetime, $cacheDiscriminator)
     {
         $metadata = implode(',', $tags);
         if ($lifetime !== null) {
diff --git a/Neos.Fusion/composer.json b/Neos.Fusion/composer.json
index 1bfe2c2a6a8..b45903a5e26 100644
--- a/Neos.Fusion/composer.json
+++ b/Neos.Fusion/composer.json
@@ -6,7 +6,7 @@
         "GPL-3.0-or-later"
     ],
     "require": {
-        "php": "^7.3",
+        "php": "^7.3 || ^8.0",
         "neos/flow": "*",
         "neos/fluid-adaptor": "*",
         "neos/cache": "*",
diff --git a/Neos.Media.Browser/composer.json b/Neos.Media.Browser/composer.json
index 9bdc413af8a..b224454b28e 100644
--- a/Neos.Media.Browser/composer.json
+++ b/Neos.Media.Browser/composer.json
@@ -6,7 +6,7 @@
         "GPL-3.0-or-later"
     ],
     "require": {
-        "php": "^7.3",
+        "php": "^7.3 || ^8.0",
         "neos/media": "self.version",
         "neos/content-repository": "self.version",
         "neos/neos": "self.version",
@@ -15,7 +15,7 @@
         "neos/utility-files": "*",
         "neos/utility-mediatypes": "*",
         "neos/error-messages": "*",
-        "doctrine/common": "^2.7",
+        "doctrine/common": "^2.7 || ^3.0",
         "doctrine/orm": "^2.6"
     },
     "autoload": {
diff --git a/Neos.Media/Classes/Security/Authorization/Privilege/Doctrine/AssetAssetCollectionConditionGenerator.php b/Neos.Media/Classes/Security/Authorization/Privilege/Doctrine/AssetAssetCollectionConditionGenerator.php
index ff6b04d1d79..0112b309dfc 100644
--- a/Neos.Media/Classes/Security/Authorization/Privilege/Doctrine/AssetAssetCollectionConditionGenerator.php
+++ b/Neos.Media/Classes/Security/Authorization/Privilege/Doctrine/AssetAssetCollectionConditionGenerator.php
@@ -11,7 +11,7 @@
  * source code.
  */
 
-use Doctrine\Common\Persistence\Mapping\ClassMetadata;
+use Doctrine\Persistence\Mapping\ClassMetadata;
 use Doctrine\ORM\EntityManagerInterface;
 use Doctrine\ORM\Query\Filter\SQLFilter as DoctrineSqlFilter;
 use Neos\Flow\Annotations as Flow;
diff --git a/Neos.Media/Classes/Security/Authorization/Privilege/Doctrine/AssetTagConditionGenerator.php b/Neos.Media/Classes/Security/Authorization/Privilege/Doctrine/AssetTagConditionGenerator.php
index 0c8c6006715..1a27881dcd8 100644
--- a/Neos.Media/Classes/Security/Authorization/Privilege/Doctrine/AssetTagConditionGenerator.php
+++ b/Neos.Media/Classes/Security/Authorization/Privilege/Doctrine/AssetTagConditionGenerator.php
@@ -11,7 +11,7 @@
  * source code.
  */
 
-use Doctrine\Common\Persistence\Mapping\ClassMetadata;
+use Doctrine\Persistence\Mapping\ClassMetadata;
 use Doctrine\ORM\EntityManagerInterface;
 use Doctrine\ORM\Query\Filter\SQLFilter as DoctrineSqlFilter;
 use Neos\Flow\Annotations as Flow;
diff --git a/Neos.Media/Classes/Security/Authorization/Privilege/Doctrine/AssetWithoutAssetCollectionConditionGenerator.php b/Neos.Media/Classes/Security/Authorization/Privilege/Doctrine/AssetWithoutAssetCollectionConditionGenerator.php
index 39d622db28c..a786aa8fa24 100644
--- a/Neos.Media/Classes/Security/Authorization/Privilege/Doctrine/AssetWithoutAssetCollectionConditionGenerator.php
+++ b/Neos.Media/Classes/Security/Authorization/Privilege/Doctrine/AssetWithoutAssetCollectionConditionGenerator.php
@@ -11,7 +11,7 @@
  * source code.
  */
 
-use Doctrine\Common\Persistence\Mapping\ClassMetadata;
+use Doctrine\Persistence\Mapping\ClassMetadata;
 use Doctrine\ORM\EntityManagerInterface;
 use Doctrine\ORM\Query\Filter\SQLFilter as DoctrineSqlFilter;
 use Neos\Flow\Annotations as Flow;
diff --git a/Neos.Media/composer.json b/Neos.Media/composer.json
index 4f758bf834c..5e0cea78686 100644
--- a/Neos.Media/composer.json
+++ b/Neos.Media/composer.json
@@ -6,7 +6,7 @@
         "GPL-3.0-or-later"
     ],
     "require": {
-        "php": "^7.3",
+        "php": "^7.3 || ^8.0",
         "neos/imagine": "^3.1.0",
         "neos/flow": "*",
         "neos/cache": "*",
@@ -14,7 +14,7 @@
         "neos/utility-objecthandling": "*",
         "neos/utility-arrays": "*",
         "imagine/imagine": "*",
-        "doctrine/common": "^2.7",
+        "doctrine/common": "^2.7 || ^3.0",
         "doctrine/orm": "^2.6",
         "doctrine/dbal": "^2.8"
     },
@@ -123,4 +123,4 @@
             "Neos.Flow-20201109224100"
         ]
     }
-}
\ No newline at end of file
+}
diff --git a/Neos.Neos/composer.json b/Neos.Neos/composer.json
index 73ff4ac08b5..97fdb217236 100644
--- a/Neos.Neos/composer.json
+++ b/Neos.Neos/composer.json
@@ -6,7 +6,7 @@
     ],
     "description": "An open source Content Application Platform based on Flow. A set of core Content Management features is resting within a larger context that allows you to build a perfectly customized experience for your users.",
     "require": {
-        "php": "^7.3",
+        "php": "^7.3 || ^8.0",
         "neos/diff": "~7.1.0",
         "neos/flow": "~7.1.0",
         "neos/media-browser": "~7.1.0",
diff --git a/Neos.NodeTypes.Form/composer.json b/Neos.NodeTypes.Form/composer.json
index a6afa7af1de..15876766cc7 100644
--- a/Neos.NodeTypes.Form/composer.json
+++ b/Neos.NodeTypes.Form/composer.json
@@ -6,7 +6,7 @@
         "GPL-3.0-or-later"
     ],
     "require": {
-        "php": "^7.3",
+        "php": "^7.3 || ^8.0",
         "neos/neos": "*",
         "neos/form": "*",
         "neos/nodetypes-basemixins": "*"
diff --git a/Neos.SiteKickstarter/composer.json b/Neos.SiteKickstarter/composer.json
index 853bdad23d8..f22aca94b08 100755
--- a/Neos.SiteKickstarter/composer.json
+++ b/Neos.SiteKickstarter/composer.json
@@ -4,7 +4,7 @@
     "description": "A simple generator for Neos assets, like sites and plugins.",
     "license": ["GPL-3.0-or-later"],
     "require": {
-        "php": "^7.3",
+        "php": "^7.3 || ^8.0",
         "neos/flow": "*",
         "neos/utility-files": "*",
         "neos/fluid-adaptor": "*",
diff --git a/composer.json b/composer.json
index 8ab5ea64fed..2a9b2a2b39b 100644
--- a/composer.json
+++ b/composer.json
@@ -8,7 +8,7 @@
     "require": {
         "neos/flow-development-collection": "7.1.x-dev",
         "neos/neos-setup": "^1.0",
-        "php": "^7.3",
+        "php": "^7.3 || ^8.0",
         "neos/flow": "*",
         "neos/cache": "*",
         "neos/eel": "*",
@@ -22,7 +22,7 @@
         "neos/utility-unicode": "*",
         "neos/utility-mediatypes": "*",
         "neos/error-messages": "*",
-        "doctrine/common": "^2.7",
+        "doctrine/common": "^2.7 || ^3.0",
         "neos/imagine": "^3.1.0",
         "imagine/imagine": "*",
         "doctrine/dbal": "^2.8",