This book constitutes the refereed proceedings of the 11th International Symposium on Practical Aspects of Declarative Languages, PADL 2009, held in Savannah, GA, USA, in January 2009, collocated with POPL 2009, the Symposium on Principles of Programming Languages. The 18 revised full papers presented together with 1 invited talk were carefully reviewed and selected from 48 submissions. The volume features original work emphasizing novel applications and implementation techniques for all forms of declarative concepts, including functions, relations, logic, and constraints. The papers address all current aspects of declarative programming; they are organized in topical sections on user interfaces and environments, networks and data, multi-threading and parallelism, databases and large data sets, tabling and optimization, as well as language extensions and implementation.