A method, apparatus, system, and signal-bearing medium that in an embodiment determine whether to stop execution of a program at a breakpoint based on a previous value of a variable. In another embodiment, an attribute is applied to all breakpoints in a breakpoint group. The attribute includes data that is used to decide whether to halt the program upon encountering the breakpoints or allow the program to continue to execute. In another embodiment, breakpoints are excluded or included on the basis of the thread in which the breakpoint is encountered by the program.