This book constitutes the refereed proceedings of the 9th International Symposium on Practical Aspects of Declarative Languages, PADL 2007, held in Nice, France, in January 2007, co-located with POPL 2007, the Symposium on Principles of Programming Languages. The 19 revised full papers presented together with two invited papers were carefully reviewed and selected from 58 submissions. All current aspects of declarative programming are addressed.