A discussion of bilingualism and second language learning distinguishes three types of bilingualism, namely, compound, coordinate, and sub-coordinate. A compound bilingual is an individual who learns two languages in the same environment so that he/she acquires one notion with two verbal expressions. A coordinate bilingual acquires the two languages in different contexts (e.g., home and school), so the words of the two languages belong to separate and independent systems. In a sub-coordinate bilingual, one language dominates. As illustration, language development is examined in case studies of the following Italian/English bilingual children in Italy: (1) a two-year-old whose Italian father uses both languages and whose English mother uses mostly English; (2) two sisters aged five and nine whose parents are Italian but who have always attended English-language schools; and (3) two Italian teenage boys whose mother has always spoken English to them and who have always attended English-language schools. The successes and problems faced by the children and their parents in developing bilingualism are discussed. It is concluded that in addition to biological predisposition, motivation and context play a significant role in bilingual development, and that overall, the bilingual experience is enriching. (MSE)