ECLiPSe includes a built-in debugger which debugs compiled code without metainterpreting it (i.e. the debugger is not a Prolog program which would simulate the execution of another program) and so the debugged code is not considerably slower than the not debugged one as is the case in most other Prolog systems. It also allows tracing the special ECLiPSe features. It is able to trace suspended goals, skip to the place where a suspended goal has been woken, trace event handlers, etc. and it has a comfortable user interface which can be easily connected with a windowing environment. The user can define macros of debugger commands, repeat them and set various leash modes of ports and procedures. Debugger events can be used to define conditional spy points, manipulate the goal variables etc.