This book constitutes the refereed proceedings of the 7th Asian Symposium on Programming Languages and Systems, APLAS 2009, held in Seoul, Korea, in December 2009. The 21 papers presented in this volume together with 3 invited talks were carefully reviewed and selected from 56 submissions. The papers are divided into topical sections on program analysis, transformation and optimization, type system, separation logic, logic and foundation theory, software security and verification, and software security and verification.