Welcome to the 20th Symposium on Principles and Practice of Declarative Programming - PPDP 2018! This year's symposium continues the long tradition of bringing together researchers from the various declarative programming communities, including those working in the logic, constraint, and functional programming paradigms. Our mission is to stimulate research in the use of logical formalisms and methods for specifying, performing, and analysing computations, including mechanisms for mobility, modularity, concurrency, objectorientation, security, verification and static analysis. This edition of PPDP was co-located with the 28th International Symposium on Logic-Based Program Synthesis and Transformation, LOPSTR 2018, and the 26th International Workshop on Functional and Logic Programming, WFLP 2018. The programs of PPDP and LOPSTR were overlapping, and two invited speakers were shared, fostering exchange of ideas between the two communities. |