We investigated whether children at the ages of two and three years understand that a speaker's use of the definite article specifies a referent that is in common ground between speaker and listener. An experimenter and a child engaged in joint actions in which the experimenter chose one of three similar objects of the same category to perform an action. In subsequent interactions children were asked to get "the X" or "a X". When children were instructed with the definite article they chose the shared object significantly more often than when they were instructed with the indefinite article in which case children's choice was at chance. The findings show that in their third year children use shared experiences to interpret the speaker's communicative intention underlying her referential choice. The results are discussed with respect to children's representation of linguistic categories and the role of joint action for establishing common ground.