There is a very vocal minority in the Valencian Country which pretends that Valencian is not the same language as Catalan. While there are some people who believe strongly in that, it isn't true from neither a philological/scientifical perspective nor a legal one.

Below are some sources from relevant authorities that clearly dispell this misunderstanding.

The Valencian myths page contains some perversions of official statements that are often used to claim Valencian is not Catalan.

Authority Source Text (in either Spanish/Castillian or Catalan/Valencian) Text in English

Tribunal Constitucional
(Maximum legal authority in Spanish kingdom)
75/1997 la valenciana, lengua propia de la Comunidad Valenciana y, por ello, de su Universidad, podrá ser también denominada «lengua catalana», en el ámbito universitario, sin que ello contradiga el Estatuto de Autonomía ni la Ley de la Cortes Valencianas. Valencian, the language of the Valencian Autonomous Community and, thus, its University, shall be also referred to as 'Catalan language', in the universitary scope, without this contradicting the Statue of Autonomy or the Valencian Courts Law.

Acadèmia Valenciana de la Llengua
(Maximum lingüistical authority over the Valencian variant of Catalan)
DICTAMEN SOBRE ELS PRINCIPIS I CRITERIS PER A LA DEFENSA DE LA DENOMINACIÓ I L'ENTITAT DEL VALENCIÀ 6. És un fet que a Espanya hi ha dos denominacions igualment legals per a designar esta llengua: la de valencià, establida en l'Estatut d'Autonomia de la Comunitat Valenciana, i la de català, reconeguda en els estatuts d'autonomia de Catalunya i les Illes Balears. 6. It is a fact that in Spain there are two equally legal denominations to dessignate this language: that of Valencian, stablished by the Statue of Autonomy of the Valencian Autonomous Community, and that of Catalan, recognised by the Statues of Autonomy of Catalonia and Balearic Islands.

Tribunal Superior de Justícia de la Comunitat Valenciana
(Maximum legal authority within the Valencian Autonomous Community)
330/2004, 393/2004, 518/2004 i 677/2004 [la titulación de filología catalana] avala sobradamente el conocimiento de la lengua de esa Comunidad, denominada oficialmente 'valenciana' en su Estatuto de Autonomía, y en el ámbito académico, 'catalana'. [Catalan philology titulation] amply guarantees knowledge of the language of this Community, officially called 'Valencian' in its Statue of Autonomy, and in academical context, 'Catalan'.

Universities University of València University of Alacant N/A There isn't a single University in the World that teaches "Valencian philology" as if it were a different titulation than Catalan one. Even the Universities of València and Alacant (both in Valencian Land) call it "Catalan philology" exclusively.

ISO-639 Standard Language Codes N/A Catalan is included in the standard (its codes are "cat" and "ca"). Valencian is included explicitly as an alternate name for Catalan, not as a separate language.

Wikipedia Catalan language N/A Catalan (Català) or Valencian (Valencià) is a Romance language, the national language of Andorra and co-official in several regions of Spain.

Authority	Source	Text (in either Spanish/Castillian or Catalan/Valencian)	Text in English
Tribunal Constitucional (Maximum legal authority in Spanish kingdom)	75/1997	la valenciana, lengua propia de la Comunidad Valenciana y, por ello, de su Universidad, podrá ser también denominada «lengua catalana», en el ámbito universitario, sin que ello contradiga el Estatuto de Autonomía ni la Ley de la Cortes Valencianas.	Valencian, the language of the Valencian Autonomous Community and, thus, its University, shall be also referred to as 'Catalan language', in the universitary scope, without this contradicting the Statue of Autonomy or the Valencian Courts Law.
Acadèmia Valenciana de la Llengua (Maximum lingüistical authority over the Valencian variant of Catalan)	DICTAMEN SOBRE ELS PRINCIPIS I CRITERIS PER A LA DEFENSA DE LA DENOMINACIÓ I L'ENTITAT DEL VALENCIÀ	6. És un fet que a Espanya hi ha dos denominacions igualment legals per a designar esta llengua: la de valencià, establida en l'Estatut d'Autonomia de la Comunitat Valenciana, i la de català, reconeguda en els estatuts d'autonomia de Catalunya i les Illes Balears.	6. It is a fact that in Spain there are two equally legal denominations to dessignate this language: that of Valencian, stablished by the Statue of Autonomy of the Valencian Autonomous Community, and that of Catalan, recognised by the Statues of Autonomy of Catalonia and Balearic Islands.
Tribunal Superior de Justícia de la Comunitat Valenciana (Maximum legal authority within the Valencian Autonomous Community)	330/2004, 393/2004, 518/2004 i 677/2004	[la titulación de filología catalana] avala sobradamente el conocimiento de la lengua de esa Comunidad, denominada oficialmente 'valenciana' en su Estatuto de Autonomía, y en el ámbito académico, 'catalana'.	[Catalan philology titulation] amply guarantees knowledge of the language of this Community, officially called 'Valencian' in its Statue of Autonomy, and in academical context, 'Catalan'.
Universities	University of València University of Alacant	N/A	There isn't a single University in the World that teaches "Valencian philology" as if it were a different titulation than Catalan one. Even the Universities of València and Alacant (both in Valencian Land) call it "Catalan philology" exclusively.
ISO-639 Standard	Language Codes	N/A	Catalan is included in the standard (its codes are "cat" and "ca"). Valencian is included explicitly as an alternate name for Catalan, not as a separate language.
Wikipedia	Catalan language	N/A	Catalan (Català) or Valencian (Valencià) is a Romance language, the national language of Andorra and co-official in several regions of Spain.