"The 22-year-old right-back, who recently represented Spain at the London [ Images ] Olympics [ Images ], arrives at Stamford Bridge [ Images ] following a two-year spell in France's [ Images ] Ligue 1 with Marseille," Chelsea said on their website (www.chelseafc.com).
No transfer fee or length of contract were mentioned.
Azpilicueta started his career at Osasuna, before leaving La Liga [ Images ] for Ligue 1 in 2010.
While not capped at international level, he has represented his country at age-group level since making the under-16 team in 2005.
Azpilicueta is coach Roberto Di Matteo's fifth summer signing, following Eden Hazard, Oscar, Marko Marin and Thorgan Hazard to Stamford Bridge.
He is the fourth Spanish player at the club, linking up with Juan Mata, Oriol Romeu and Fernando Torres [ Images ].
Wigan Athletic said on Thursday they have accepted Chelsea's fifth bid for their winger Victor Moses.