diff --git a/TODO b/TODO
index c217c8d6..e37e1f7d 100644
--- a/TODO
+++ b/TODO
@@ -28,16 +28,17 @@ everything related to tags:
         - tag editing
             - category (from config.ini)
             - description
-    - implications - when entering child tag, add parent tag
-        - take care of recursion
-        - listing
-            - sort alphabetically
-            - sort by time of addition
-        - adding
-        - removing
-        - editing
-            - source tag
-            - target tags (allow multiple)
+    - relations
+        - handle tag relations editing in frontend
+            - privileges
+            - template
+            - ajax
+        - handle tag relations editing in backend
+            - tagservice::update
+            - tageditformdata
+            - tagcontroller
+            - privileges
+        - handle relations in autocomplete
 
 refactors:
     - add enum validation in IValidatables (needs refactors of enums and
diff --git a/src/Dao/TagDao.php b/src/Dao/TagDao.php
index 1127f30b..0793a79d 100644
--- a/src/Dao/TagDao.php
+++ b/src/Dao/TagDao.php
@@ -3,9 +3,14 @@ namespace Szurubooru\Dao;
 use Szurubooru\Dao\EntityConverters\PostEntityConverter;
 use Szurubooru\Dao\EntityConverters\TagEntityConverter;
 use Szurubooru\DatabaseConnection;
+use Szurubooru\Entities\Entity;
+use Szurubooru\Entities\Tag;
 
 class TagDao extends AbstractDao implements ICrudDao
 {
+	const TAG_RELATION_IMPLICATION = 1;
+	const TAG_RELATION_SUGGESTION = 2;
+
 	public function __construct(DatabaseConnection $databaseConnection)
 	{
 		parent::__construct(
@@ -49,7 +54,7 @@ class TagDao extends AbstractDao implements ICrudDao
 			->disableSmartJoin()
 			->innerJoin('postTags pt1 ON pt1.tagId = tags.id')
 			->innerJoin('postTags pt2 ON pt2.postId = pt1.postId')
-			->where('pt2.tagId = ?', $tagId)
+			->where('pt2.tagId', $tagId)
 			->groupBy('tags.id')
 			->orderBy('tags.usages DESC, name ASC');
 		$arrayEntities = iterator_to_array($query);
@@ -60,4 +65,87 @@ class TagDao extends AbstractDao implements ICrudDao
 	{
 		$this->deleteBy('usages', 0);
 	}
+
+	protected function afterLoad(Entity $tag)
+	{
+		$tag->setLazyLoader(
+			Tag::LAZY_LOADER_IMPLIED_TAGS,
+			function (Tag $tag)
+			{
+				return $this->findImpliedTags($tag);
+			});
+
+		$tag->setLazyLoader(
+			Tag::LAZY_LOADER_SUGGESTED_TAGS,
+			function (Tag $tag)
+			{
+				return $this->findSuggested($tag);
+			});
+	}
+
+	protected function afterSave(Entity $tag)
+	{
+		$this->syncImpliedTags($tag);
+		$this->syncSuggestedTags($tag);
+	}
+
+	private function findImpliedTags(Tag $tag)
+	{
+		return $this->findRelatedTagsByType($tag, self::TAG_RELATION_IMPLICATION);
+	}
+
+	private function findSuggested(Tag $tag)
+	{
+		return $this->findRelatedTagsByType($tag, self::TAG_RELATION_SUGGESTION);
+	}
+
+	private function syncImpliedTags($tag)
+	{
+		$this->syncRelatedTagsByType($tag, $tag->getImpliedTags(), self::TAG_RELATION_IMPLICATION);
+	}
+
+	private function syncSuggestedTags($tag)
+	{
+		$this->syncRelatedTagsByType($tag, $tag->getSuggestedTags(), self::TAG_RELATION_SUGGESTION);
+	}
+
+	private function syncRelatedTagsByType(Tag $tag, array $relatedTags, $type)
+	{
+		$this->fpdo->deleteFrom('tagRelations')
+			->where('tag1id', $tag->getId())
+			->where('type', $type)
+			->execute();
+
+		$relatedTagIds = array_filter(array_unique(array_map(
+			function ($tag)
+			{
+				if (!$tag->getId())
+					throw new \RuntimeException('Unsaved entities found');
+				return $tag->getId();
+			},
+			$relatedTags)));
+
+		foreach ($relatedTagIds as $tagId)
+		{
+			$this->fpdo
+				->insertInto('tagRelations')
+				->values([
+					'tag1id' => $tag->getId(),
+					'tag2id' => $tagId,
+					'type' => $type])
+				->execute();
+		}
+	}
+
+	private function findRelatedTagsByType(Tag $tag, $type)
+	{
+		$tagId = $tag->getId();
+		$query = $this->fpdo->from($this->tableName)
+			->disableSmartJoin()
+			->innerJoin('tagRelations tr ON tags.id = tr.tag2id')
+			->where('tr.type', $type)
+			->where('tr.tag1id', $tagId);
+		$arrayEntities = iterator_to_array($query);
+		return $this->arrayToEntities($arrayEntities);
+	}
 }
diff --git a/src/Entities/Tag.php b/src/Entities/Tag.php
index ecd8f596..80a7b7d4 100644
--- a/src/Entities/Tag.php
+++ b/src/Entities/Tag.php
@@ -7,6 +7,9 @@ final class Tag extends Entity
 	private $creationTime;
 	private $banned = false;
 
+	const LAZY_LOADER_IMPLIED_TAGS = 'implications';
+	const LAZY_LOADER_SUGGESTED_TAGS = 'suggestions';
+
 	const META_USAGES = 'usages';
 
 	public function getName()
@@ -44,4 +47,23 @@ final class Tag extends Entity
 		return $this->getMeta(self::META_USAGES);
 	}
 
+	public function getImpliedTags()
+	{
+		return $this->lazyLoad(self::LAZY_LOADER_IMPLIED_TAGS, []);
+	}
+
+	public function setImpliedTags(array $impliedTags)
+	{
+		$this->lazySave(self::LAZY_LOADER_IMPLIED_TAGS, $impliedTags);
+	}
+
+	public function getSuggestedTags()
+	{
+		return $this->lazyLoad(self::LAZY_LOADER_SUGGESTED_TAGS, []);
+	}
+
+	public function setSuggestedTags(array $suggestedTags)
+	{
+		$this->lazySave(self::LAZY_LOADER_SUGGESTED_TAGS, $suggestedTags);
+	}
 }
diff --git a/src/Upgrades/Upgrade24.php b/src/Upgrades/Upgrade24.php
new file mode 100644
index 00000000..e3d72c02
--- /dev/null
+++ b/src/Upgrades/Upgrade24.php
@@ -0,0 +1,22 @@
+<?php
+namespace Szurubooru\Upgrades;
+use Szurubooru\DatabaseConnection;
+use Szurubooru\Services\TagService;
+
+class Upgrade24 implements IUpgrade
+{
+	public function run(DatabaseConnection $databaseConnection)
+	{
+		$pdo = $databaseConnection->getPDO();
+		$driver = $databaseConnection->getDriver();
+
+		$pdo->exec(
+			'CREATE TABLE tagRelations (
+				id INTEGER PRIMARY KEY ' . ($driver === 'mysql' ? 'AUTO_INCREMENT' : 'AUTOINCREMENT') . ',
+				tag1id INTEGER NOT NULL,
+				tag2id INTEGER NOT NULL,
+				type INTEGER(2) NOT NULL,
+				UNIQUE (tag1id, tag2id, type)
+			)');
+	}
+}
diff --git a/src/di.php b/src/di.php
index 2d040a95..baa74639 100644
--- a/src/di.php
+++ b/src/di.php
@@ -39,6 +39,7 @@ return [
 			$container->get(\Szurubooru\Upgrades\Upgrade21::class),
 			$container->get(\Szurubooru\Upgrades\Upgrade22::class),
 			$container->get(\Szurubooru\Upgrades\Upgrade23::class),
+			$container->get(\Szurubooru\Upgrades\Upgrade24::class),
 		];
 	}),
 
diff --git a/tests/Dao/TagDaoTest.php b/tests/Dao/TagDaoTest.php
index a054da4b..b82e68c6 100644
--- a/tests/Dao/TagDaoTest.php
+++ b/tests/Dao/TagDaoTest.php
@@ -25,6 +25,45 @@ final class TagDaoTest extends AbstractDatabaseTestCase
 		$this->assertEntitiesEqual($tag, $actualTag);
 	}
 
+	public function testSavingRelations()
+	{
+		$tag1 = new Tag();
+		$tag1->setName('test 1');
+		$tag1->setCreationTime(date('c'));
+		$tag2 = new Tag();
+		$tag2->setName('test 2');
+		$tag2->setCreationTime(date('c'));
+		$tag3 = new Tag();
+		$tag3->setName('test 3');
+		$tag3->setCreationTime(date('c'));
+		$tag4 = new Tag();
+		$tag4->setName('test 4');
+		$tag4->setCreationTime(date('c'));
+		$tagDao = $this->getTagDao();
+		$tagDao->save($tag1);
+		$tagDao->save($tag2);
+		$tagDao->save($tag3);
+		$tagDao->save($tag4);
+
+		$tag = new Tag();
+		$tag->setName('test1');
+		$tag->setCreationTime(date('c'));
+		$tag->setImpliedTags([$tag1, $tag3]);
+		$tag->setSuggestedTags([$tag2, $tag4]);
+
+		$this->assertGreaterThan(0, count($tag->getImpliedTags()));
+		$this->assertGreaterThan(0, count($tag->getSuggestedTags()));
+
+		$tagDao->save($tag);
+		$actualTag = $tagDao->findById($tag->getId());
+
+		$this->assertEntitiesEqual($tag, $actualTag);
+		$this->assertEntitiesEqual(array_values($tag->getImpliedTags()), array_values($actualTag->getImpliedTags()));
+		$this->assertEntitiesEqual(array_values($tag->getSuggestedTags()), array_values($actualTag->getSuggestedTags()));
+		$this->assertGreaterThan(0, count($actualTag->getImpliedTags()));
+		$this->assertGreaterThan(0, count($actualTag->getSuggestedTags()));
+	}
+
 	public function testFindByPostIds()
 	{
 		$pdo = $this->databaseConnection->getPDO();