This chapter provides an overview of how linguists analyse and attempt to explain the acquisition of English pronunciation patterns by adult learners. Virtually all linguists who study the acquisition of a language by either children or adults postulate that learners internalize a system that represents their own version of the ambient or target language. This system, termed an interlanguage in the case of second language (L2) learners, is used by these acquirers to produce and comprehend utterances of the language being learned. The goal of language acquisition research thereby becomes the characterization and explanation of these learner systems. This chapter gives a brief account of some of the major proposals that linguists have made in the last sixty years in attempting to explain English L2 phonological patterns.