diff --git a/lib/Collection.php b/lib/Collection.php
index 87b97e06..8c6b8a95 100644
--- a/lib/Collection.php
+++ b/lib/Collection.php
@@ -7,9 +7,9 @@ use function Safe\preg_replace;
 class Collection{
 	use Traits\Accessor;
 
+	public int $CollectionId;
 	public string $Name;
 	public string $UrlName;
-	public ?int $SequenceNumber = null;
 	public ?string $Type = null;
 	protected ?string $_Url = null;
 
@@ -28,7 +28,77 @@ class Collection{
 		return $instance;
 	}
 
+	/**
+	 * @throws Exceptions\CollectionNotFoundException
+	 */
+	public static function Get(?int $collectionId): Collection{
+		if($collectionId === null){
+			throw new Exceptions\CollectionNotFoundException();
+		}
+
+		$result = Db::Query('
+				SELECT *
+				from Collections
+				where CollectionId = ?
+			', [$collectionId], Collection::class);
+
+		return $result[0] ?? throw new Exceptions\CollectionNotFoundException();;
+	}
+
 	public function GetSortedName(): string{
 		return preg_replace('/^(the|and|a|)\s/ius', '', $this->Name);
 	}
+
+	/**
+	 * @throws Exceptions\ValidationException
+	 */
+	public function Validate(): void{
+		$error = new Exceptions\ValidationException();
+
+		if(strlen($this->Name) > EBOOKS_MAX_STRING_LENGTH){
+			$error->Add(new Exceptions\StringTooLongException('Collection name: '. $this->Name));
+		}
+
+		if($this->Type !== null && ($this->Type != 'series' && $this->Type != 'set')){
+			$error->Add(new Exceptions\InvalidCollectionTypeException($this->Type));
+		}
+
+		if($error->HasExceptions){
+			throw $error;
+		}
+	}
+
+	/**
+	 * @throws Exceptions\ValidationException
+	 */
+	public function Create(): void{
+		$this->Validate();
+
+		Db::Query('
+			INSERT into Collections (Name, UrlName, Type)
+			values (?,
+				?,
+				?)
+		', [$this->Name, $this->UrlName, $this->Type]);
+		$this->CollectionId = Db::GetLastInsertedId();
+	}
+
+	/**
+	 * @throws Exceptions\ValidationException
+	 */
+	public function GetByUrlNameOrCreate(string $urlName): Collection{
+		$result = Db::Query('
+				SELECT *
+				from Collections
+				where UrlName = ?
+			', [$urlName], Collection::class);
+
+		if(isset($result[0])){
+			return $result[0];
+		}
+		else{
+			$this->Create();
+			return $this;
+		}
+	}
 }
diff --git a/lib/CollectionMembership.php b/lib/CollectionMembership.php
new file mode 100644
index 00000000..7ded2833
--- /dev/null
+++ b/lib/CollectionMembership.php
@@ -0,0 +1,12 @@
+<?
+use function Safe\preg_replace;
+
+/**
+ * @property Collection $Collection
+ */
+class CollectionMembership{
+	use Traits\Accessor;
+
+	public ?int $SequenceNumber = null;
+	protected ?Collection $_Collection = null;
+}
diff --git a/lib/Ebook.php b/lib/Ebook.php
index 381df37a..83f718af 100644
--- a/lib/Ebook.php
+++ b/lib/Ebook.php
@@ -15,7 +15,7 @@ use function Safe\shell_exec;
  * @property array<GitCommit> $GitCommits
  * @property array<EbookTag> $Tags
  * @property array<LocSubject> $LocSubjects
- * @property array<Collection> $Collections
+ * @property array<CollectionMembership> $CollectionMemberships
  * @property array<EbookSource> $Sources
  * @property array<Contributor> $Authors
  * @property array<Contributor> $Illustrators
@@ -76,8 +76,8 @@ class Ebook{
 	protected $_Tags = null;
 	/** @var array<LocSubject> $_LocSubjects */
 	protected $_LocSubjects = null;
-	/** @var array<Collection> $_Collections */
-	protected $_Collections = null;
+	/** @var array<CollectionMembership> $_CollectionMemberships */
+	protected $_CollectionMemberships = null;
 	/** @var array<EbookSource> $_Sources */
 	protected $_Sources = null;
 	/** @var array<Contributor> $_Authors */
@@ -167,18 +167,19 @@ class Ebook{
 	}
 
 	/**
-	 * @return array<Collection>
+	 * @return array<CollectionMembership>
 	 */
-	protected function GetCollections(): array{
-		if($this->_Collections === null){
-			$this->_Collections = Db::Query('
+	protected function GetCollectionMemberships(): array{
+		if($this->_CollectionMemberships === null){
+			$this->_CollectionMemberships = Db::Query('
 							SELECT *
-							from Collections
+							from CollectionEbooks
 							where EbookId = ?
-						', [$this->EbookId], Collection::class);
+							order by CollectionEbookId
+						', [$this->EbookId], CollectionMembership::class);
 		}
 
-		return $this->_Collections;
+		return $this->_CollectionMemberships;
 	}
 
 	/**
@@ -549,8 +550,8 @@ class Ebook{
 
 			$this->_IndexableText .= ' ' . $this->AlternateTitle;
 
-			foreach($this->Collections as $collection){
-				$this->_IndexableText .= ' ' . $collection->Name;
+			foreach($this->CollectionMemberships as $collectionMembership){
+				$this->_IndexableText .= ' ' . $collectionMembership->Collection->Name;
 			}
 
 			foreach($this->Authors as $author){
@@ -749,20 +750,21 @@ class Ebook{
 		}
 
 		// Get SE collections
-		$collections = [];
+		$collectionMemberships = [];
 		foreach($xml->xpath('/package/metadata/meta[@property="belongs-to-collection"]') ?: [] as $collection){
-			$c = Collection::FromName($collection);
-			$id = $collection->attributes()->id ?? '';
+			$cm = new CollectionMembership();
+			$cm->Collection = Collection::FromName($collection);
 
+			$id = $collection->attributes()->id ?? '';
 			foreach($xml->xpath('/package/metadata/meta[@refines="#' . $id . '"][@property="group-position"]') ?: [] as $s){
-				$c->SequenceNumber = (int)$s;
+				$cm->SequenceNumber = (int)$s;
 			}
 			foreach($xml->xpath('/package/metadata/meta[@refines="#' . $id . '"][@property="collection-type"]') ?: [] as $s){
-				$c->Type = (string)$s;
+				$cm->Collection->Type = (string)$s;
 			}
-			$collections[] = $c;
+			$collectionMemberships[] = $cm;
 		}
-		$ebookFromFilesystem->Collections = $collections;
+		$ebookFromFilesystem->CollectionMemberships = $collectionMemberships;
 
 		// Get LoC tags
 		$locSubjects = [];
@@ -1125,10 +1127,25 @@ class Ebook{
 		$this->LocSubjects = $subjects;
 	}
 
+	/**
+	 * @throws Exceptions\ValidationException
+	 */
+	private function InsertCollections(): void{
+		$collectionMemberships = [];
+		foreach($this->CollectionMemberships as $collectionMembership){
+			$collection = $collectionMembership->Collection;
+			// The updated collection has the CollectionId set for newly-created Collection objects.
+			$updatedCollection = $collection->GetByUrlNameOrCreate($collection->UrlName);
+			$collectionMembership->Collection = $updatedCollection;
+			$collectionMemberships[] = $collectionMembership;
+		}
+		$this->CollectionMemberships = $collectionMemberships;
+	}
+
 	public function GetCollectionPosition(Collection $collection): ?int{
-		foreach($this->Collections as $c){
-			if($c->Name == $collection->Name){
-				return $c->SequenceNumber;
+		foreach($this->CollectionMemberships as $cm){
+			if($cm->Collection->Name == $collection->Name){
+				return $cm->SequenceNumber;
 			}
 		}
 
@@ -1143,8 +1160,8 @@ class Ebook{
 
 		$searchString .= ' ' . $this->AlternateTitle;
 
-		foreach($this->Collections as $collection){
-			$searchString .= ' ' . $collection->Name;
+		foreach($this->CollectionMemberships as $collectionMembership){
+			$searchString .= ' ' . $collectionMembership->Collection->Name;
 		}
 
 		foreach($this->Authors as $author){
@@ -1414,8 +1431,8 @@ class Ebook{
 	}
 
 	public function IsInCollection(string $collection): bool{
-		foreach($this->Collections as $c){
-			if(strtolower(Formatter::RemoveDiacritics($c->Name)) == strtolower(Formatter::RemoveDiacritics($collection))){
+		foreach($this->CollectionMemberships as $cm){
+			if(strtolower(Formatter::RemoveDiacritics($cm->Collection->Name)) == strtolower(Formatter::RemoveDiacritics($collection))){
 				return true;
 			}
 		}
@@ -1456,6 +1473,7 @@ class Ebook{
 
 		$this->InsertTagStrings();
 		$this->InsertLocSubjectStrings();
+		$this->InsertCollections();
 
 		Db::Query('
 			INSERT into Ebooks (Identifier, WwwFilesystemPath, RepoFilesystemPath, KindleCoverUrl, EpubUrl,
@@ -1495,8 +1513,8 @@ class Ebook{
 
 		$this->InsertTags();
 		$this->InsertLocSubjects();
+		$this->InsertCollectionMemberships();
 		$this->InsertGitCommits();
-		$this->InsertCollections();
 		$this->InsertSources();
 		$this->InsertContributors();
 		$this->InsertTocEntries();
@@ -1510,6 +1528,7 @@ class Ebook{
 
 		$this->InsertTagStrings();
 		$this->InsertLocSubjectStrings();
+		$this->InsertCollections();
 
 		Db::Query('
 			UPDATE Ebooks
@@ -1552,12 +1571,12 @@ class Ebook{
 		$this->DeleteLocSubjects();
 		$this->InsertLocSubjects();
 
+		$this->DeleteCollectionMemberships();
+		$this->InsertCollectionMemberships();
+
 		$this->DeleteGitCommits();
 		$this->InsertGitCommits();
 
-		$this->DeleteCollections();
-		$this->InsertCollections();
-
 		$this->DeleteSources();
 		$this->InsertSources();
 
@@ -1606,6 +1625,26 @@ class Ebook{
 		}
 	}
 
+	private function DeleteCollectionMemberships(): void{
+		Db::Query('
+			DELETE from CollectionEbooks
+			where
+			EbookId = ?
+		', [$this->EbookId]
+		);
+	}
+
+	private function InsertCollectionMemberships(): void{
+		foreach($this->CollectionMemberships as $collectionMembership){
+			Db::Query('
+				INSERT into CollectionEbooks (EbookId, CollectionId, SequenceNumber)
+				values (?,
+					?,
+				        ?)
+			', [$this->EbookId, $collectionMembership->Collection->CollectionId, $collectionMembership->SequenceNumber]);
+		}
+	}
+
 	private function DeleteGitCommits(): void{
 		Db::Query('
 			DELETE from GitCommits
@@ -1627,28 +1666,6 @@ class Ebook{
 		}
 	}
 
-	private function DeleteCollections(): void{
-		Db::Query('
-			DELETE from Collections
-			where
-			EbookId = ?
-		', [$this->EbookId]
-		);
-	}
-
-	private function InsertCollections(): void{
-		foreach($this->Collections as $collection){
-			Db::Query('
-				INSERT into Collections (EbookId, Name, UrlName, SequenceNumber, Type)
-				values (?,
-					?,
-					?,
-					?,
-				        ?)
-			', [$this->EbookId, $collection->Name, $collection->UrlName, $collection->SequenceNumber, $collection->Type]);
-		}
-	}
-
 	private function DeleteSources(): void{
 		Db::Query('
 			DELETE from EbookSources
diff --git a/lib/Exceptions/InvalidCollectionTypeException.php b/lib/Exceptions/InvalidCollectionTypeException.php
new file mode 100644
index 00000000..7d7f3334
--- /dev/null
+++ b/lib/Exceptions/InvalidCollectionTypeException.php
@@ -0,0 +1,16 @@
+<?php
+
+namespace Exceptions;
+
+class InvalidCollectionTypeException extends AppException{
+	/** @var string $message */
+	protected $message = 'Collection type should be `series` or `set` according to the EPUB specification.';
+
+	public function __construct(?string $collectionType){
+		if($collectionType !== null && trim($collectionType) != ''){
+			$this->message .= ' Type provided: ' . $collectionType;
+		}
+
+		parent::__construct($this->message);
+	}
+}
diff --git a/lib/Library.php b/lib/Library.php
index 435bad62..a8193204 100644
--- a/lib/Library.php
+++ b/lib/Library.php
@@ -163,9 +163,11 @@ class Library{
 	public static function GetEbooksByCollection(string $collection): array{
 		$ebooks = Db::Query('
 				SELECT e.*
-				from Ebooks e inner join Collections c using (EbookId)
+				from Ebooks e
+				inner join CollectionEbooks ce using (EbookId)
+				inner join Collections c using (CollectionId)
 				where c.UrlName = ?
-				order by c.SequenceNumber, e.Title
+				order by ce.SequenceNumber, e.EbookCreated desc
 				', [$collection], Ebook::class);
 
 		return $ebooks;
@@ -708,7 +710,9 @@ class Library{
 				$ebooks[$ebookWwwFilesystemPath] = $ebook;
 
 				// Create the collections cache
-				foreach($ebook->Collections as $collection){
+				foreach($ebook->CollectionMemberships as $collectionMembership){
+					$collection = $collectionMembership->Collection;
+					$sequenceNumber = $collectionMembership->SequenceNumber;
 					$urlSafeCollection = Formatter::MakeUrlSafe($collection->Name);
 					if(!array_key_exists($urlSafeCollection, $ebooksByCollection)){
 						$ebooksByCollection[$urlSafeCollection] = [];
@@ -721,8 +725,8 @@ class Library{
 					// then later we sort by that instead of by array index.
 					$sortItem = new stdClass();
 					$sortItem->Ebook = $ebook;
-					if($collection->SequenceNumber !== null){
-						$sortItem->Ordinal = $collection->SequenceNumber;
+					if($sequenceNumber !== null){
+						$sortItem->Ordinal = $sequenceNumber;
 					}
 					else{
 						$sortItem->Ordinal = 1;
diff --git a/www/collections/get.php b/www/collections/get.php
index 0124169a..5d7a808c 100644
--- a/www/collections/get.php
+++ b/www/collections/get.php
@@ -10,7 +10,8 @@ try{
 	$ebooks = Library::GetEbooksByCollection($collection);
 	// Get the *actual* name of the collection, in case there are accent marks (like "Arsène Lupin")
 	if(sizeof($ebooks) > 0){
-		foreach($ebooks[0]->Collections as $c){
+		foreach($ebooks[0]->CollectionMemberships as $cm){
+			$c = $cm->Collection;
 			if($collection == Formatter::MakeUrlSafe($c->Name)){
 				$collectionObject = $c;
 			}
diff --git a/www/ebooks/ebook.php b/www/ebooks/ebook.php
index 8612719a..766c3668 100644
--- a/www/ebooks/ebook.php
+++ b/www/ebooks/ebook.php
@@ -148,9 +148,11 @@ catch(Exceptions\EbookNotFoundException){
 			<? if($ebook->ContributorsHtml !== null){ ?>
 				<p><?= $ebook->ContributorsHtml ?></p>
 			<? } ?>
-			<? if(sizeof($ebook->Collections) > 0){ ?>
-				<? foreach($ebook->Collections as $collection){ ?>
-					<p><? if($collection->SequenceNumber !== null){ ?>№ <?= number_format($collection->SequenceNumber) ?> in the<? }else{ ?>Part of the<? } ?> <a href="<?= $collection->Url ?>" property="schema:isPartOf"><?= Formatter::EscapeHtml(preg_replace('/^The /ius', '', (string)$collection->Name)) ?></a>
+			<? if(sizeof($ebook->CollectionMemberships) > 0){ ?>
+				<? foreach($ebook->CollectionMemberships as $collectionMembership){ ?>
+					<? $collection = $collectionMembership->Collection; ?>
+					<? $sequenceNumber = $collectionMembership->SequenceNumber; ?>
+					<p><? if($sequenceNumber !== null){ ?>№ <?= number_format($sequenceNumber) ?> in the<? }else{ ?>Part of the<? } ?> <a href="<?= $collection->Url ?>" property="schema:isPartOf"><?= Formatter::EscapeHtml(preg_replace('/^The /ius', '', (string)$collection->Name)) ?></a>
 					<? if($collection->Type !== null){ ?>
 						<? if(substr_compare(mb_strtolower($collection->Name), mb_strtolower($collection->Type), -strlen(mb_strtolower($collection->Type))) !== 0){ ?>
 							<?= $collection->Type ?>.