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, colocated with POPL 2007, the Symposium on Principles of Programming Languages.The 19 revised full papers presented together with 2 invited papers were carefully reviewed and selected from 58 submissions. All current aspects of declarative programming are addressed including implementational issues and innovative applications in areas such as database management, software engineering, functional logic, decision support systems, constraint programming, model checking, probabilistic programming, Java and Prolog programming.