This volume contains the papers presented at the 1999 International C- ference on Principles and Practice of Declarative Programming (PPDP'99) held in Paris from September 29 through October 1, 1999. PPDP'99 participated, together with the International Conference on Functional Programming (ICFP) and several related workshops, in a federation of colloquia known as Principles, Logics and Implementations of high-level programming languages(PLI'99)...