This research concerns language maintenance and shift by adult speakers of Catalan and Spanish in Barcelona. Data was collected in 1991 and in 2000, through personal interviews and questionnaires, with the aim of understanding individual sociolinguistic situations and language choices. In this paper language shift behavior by individual speakers is viewed as linguistic mobility. The paper discusses the concept of shift, what kinds of behaviors constitute shift and indications of shift in the present data. Shift behavior is reported by both L1 Catalan speakers and L1 Spanish speakers. Amounts of Catalan compared to amounts of Spanish used, changes in amounts of use, choice of language with the same L1 group members and other L1 group members are presented. Findings of language shift by participants' family members are included. The findings are also considered in relationship to the concept of linguistic markets (Bourdieu 1977, 1982, 1991).