This article presents theoretical considerations behind the Jyvaskyla teacher in-service development program in teaching content through a foreign language and surveys some international experiences of bilingual education. The term "bilingual program" refers to all variations of bilingual education and teaching of non-language subjects through the second/foreign language, from total immersion to short, content-based courses. The ultimate aim of second language learning is some level of bilingualism, a complex concept to define. Definitions of bilingualism use the criterion of competence level, age or origin, the learning process, the individual's identification with the two languages, or the functions that the two languages have in his environment. Finns regard the ability to speak the language articulately as the main indicator of language proficiency. Language learning presupposes cognitive processing of input and real-life testing of the hypotheses formed. Various factors are involved in communicative competence; in Finland, teaching non-language subjects through a foreign language is referred to as immersion, foreign language content instruction, content-based language instruction, extended language instruction or language-enhanced content instruction. European models of bilingual education and considerations on the development of bilingual education are discussed. (Contains 43 references.) (CK)