This book, complete with online files and updates, covers a hugely important area of study in computing. It constitutes the refereed proceedings of the 10th International Symposium on Practical Aspects of Declarative Languages, PADL 2008, held in San Francisco, CA, USA, in January 2008. The 20 revised full papers along with the abstract of 1 invited talk were carefully reviewed and selected from 44 submissions. The papers address all current aspects of declarative programming.