In several of the most widely read Spanish grammars an entire chapter is devoted to the two copular verbs in Spanish, ser “to be” and estar “to be”, and their many contexts of use (Bull, 1965; Solé and Solé, 1977; Whitley, 1986; Bosque and Demonte, 1999; King and Suñer, 1999; Butt and Benjamin, 2000). For some, the interest in this structure stems from the range of meanings that can be expressed with these two forms, whereas for others it is the variability in the use of these verbs with adjectives, existing between groups, individuals and particular social contexts, that generates inquiry. The combination of these two traits makes the contrast difficult to acquire and likely to be lost or weakened in contexts of language attrition or language contact (Silva-Corvalán, 1986; Geeslin, 2002) and this complexity makes the copula contrast in Spanish an excellent mechanism for exploring broader issues such as theories of acquisition and language change, which are of value to a readership well beyond those working directly on Spanish. After a brief description of the distribution of ser and estar, we provide an overview of the various theoretical descriptions of the copula contrast that exist and their implications for research on bilingualism. Next, we provide a description of the papers in this volume, and outline the areas of interest for readers whose research extends beyond Spanish grammar.