This thematic issue explores various aspects of interlanguage phonetics and phonology and their relationship to general linguistic theory. Research in interlanguage syntax and recently in discourse and pragmatics has been quite prolific; however, research in interlanguage phonetics and phonology has produced far fewer studies. Of the nearly 200 articles published in Studies in Second Language Acquisition (SSLA) during the last 10 years, only about a dozen focus on phonetics and phonology. This thematic issue is intended to fill some of this gap.