A debugger for aiding in the debugging of multi-threaded program, in response to an event such as, for example, a breakpoint in a thread which has caused an operating system to stop execution of all threads, identifies the thread which contained the breakpoint. After identifying the thread which contained the breakpoint, the debugger enables the operating system to resume execution of the other threads, that is, the threads which did not contain the breakpoint. By allowing the other threads, that is, the threads which did not contain the breakpoint, to continue execution, the debugger's impact on program execution is substantially reduced, particularly for programs which contain a large number of threads.