Declarative languages build on sound theoretical bases to provide attractive frameworks for application development. These languages have been succe- fully applied to a wide variety of real-world situations including database m- agement, active networks, software engineering, and decision-support systems. New developments in theory and implementation expose fresh opportunities. At the same time, the application of declarative languages to novel problems raises numerous interesting research issues. These well-known questions include scalability, language extensions for application deployment, and programming environments. Thus, applications drive the progress in the theory and imp- mentation of declarative systems, and in turn bene?t from this progress. The International Symposium on Practical Applications of Declarative L- guages (PADL) provides a forum for researchers, practitioners, and implementors of declarative languages to exchange ideas on current and novel application - eas and on the requirements for e?ective use of declarative systems. The fourth PADL symposium was held in Portland, Oregon, on January 19 and 20, 2002.