|Full name||Xabier Castillo Aranburu|
|Date of birth||29 March 1986|
|Place of birth||Durango, Spain|
|Height||1.84 m (6 ft 0 in)|
|Playing position||Left back|
|2004–2006||Real Sociedad B||55||(2)|
|2006–2007||→ Las Palmas (loan)||31||(0)|
* Senior club appearances and goals counted for the domestic league only and correct as of 7 June 2015.
Born in Durango, Biscay, Castillo came up through the ranks at Athletic Bilbao, but made his senior debuts with Basque neighbours Real Sociedad, where he had finished his football grooming. His first professional experience came with UD Las Palmas on loan, in 2006–07's second division; during his first two seasons with Real Sociedad's first team he was an undisputed first-choice, also in the second level.
On 15 July 2009 Castillo returned his first alma mater, signing a four-year deal. He made his La Liga debut in the campaign opener (30 August 2009), a 1–0 home win against RCD Espanyol, and appeared in 45 official games in his first two years combined.
Castillo spent the entire 2011–12 on the sidelines, due to a patellar ligament injury. Upon returning he was only a fringe player, being released by the Marcelo Bielsa-led squad in June 2013 after his contract expired and returning to former team Las Palmas.
- Signing of Xabi Castillo; Athletic's official website, 15 July 2009
- Athletic Bilbao 1–0 Espanyol; ESPN Soccernet, 30 August 2009
- Xabi Castillo, operado con éxito (Xabi Castillo, surgery was a success); Marca, 22 December 2011 (Spanish)
- Tratamiento distinto para Xabi Castillo (Different treatment for Xabi Castillo); El Mundo Deportivo, 23 May 2013 (Spanish)
- Athletic no se despide de Bielsa, Llorente y Amorebieta (Athletic does not say goodbye to Bielsa, Llorente and Amorebieta); Goal.com, 22 June 2013 (Spanish)
- Xabi Castillo vuelve a Las Palmas (Xabi Castillo returns to Las Palmas); Canarias7, 10 July 2013 (Spanish)
- El Deportivo Alavés ficha a Xabi Castillo (Deportivo Alavés signs Xabi Castillo); Alavés' official website, 10 July 2014 (Spanish)