Prolog interpreter ISO/Edinburgh-style Prolog compiler. Compliant with Part 1 of the ISO standard for Prolog. Covers all traditional Edinburgh Prolog features and shares many features with Quintus and SICStus Prolog, including a compatible module system. Very fast compiler, garbage collection (also on atoms), fast and powerful C/C++ interface, autoloading, GNU-readline interface. SWI-Prolog has been designed and implemented such that it can easily be modified for experiments with logic programming and the relation between logic programming and other programming paradigms (such as the object oriented XPCE environment). SWI-Prolog has a rich set of built-in predicates and reasonable performance, which makes it possible to develop substantial applications in it. The current version offers a module system, garbage collection and an interface to the C language.