In communication speakers take into account normative expectations acquired in the course of socialization which allow them to anticipate the consequences of their linguistic choices. So far, we have discussed a number of social variables that affect choices, including the choice of codes which may be different languages or dialects of the same language. The range of choices is variable, but that speakers can and have to choose from more than one code is very common, both in bilingual societies and in monolingual ones whose members think of themselves as making choices between two noticeably diverse varieties of one language. In a number of cases, choice of these varieties does not depend on region, class, gender or age, but primarily on function and context. Such a configuration is known as ‘diglossia’. In this chapter we will first examine the specifics of a diglossic situation and then compare it with other forms of societal bilingualism.