This paper presents an overview of phonological relationships that are “intermediate” between contrast and allophony. As has been observed for many years, such intermediate relationships occur widely in the world's languages, yet they are often simply relegated to being exceptional cases or ignored in linguistic analyses. While there is a set of criteria that can be used to define relationships, these criteria may conflict with one another or be inadequate in certain cases. Thus, relationships may be intermediate for a number of reasons, including issues with: the concept of predictability of distribution; the existence of foreign or specialized strata of a language; variability and gradience; frequency; theory-internal classifications; and phonetic factors. Each of these is discussed in turn, with examples from the literature. In addition to this basic typology of intermediate phonological relationships, the paper also lays out a number of different kinds of approaches that have been taken to accommodate intermediate relationships in the phonological grammar and summarizes the issues to be resolved in future work.