Visual representations of multiple call stacks in a parallel programming system include a stack segments graph constructed by coalescing data from multiple stacks. The graph has nodes that represent stack segments and has arcs between adjacent segments. Similar stack frames are represented by the same node. In a stack prefix view of the graph, arcs are directed from a node representing stack frames to a node representing subsequently executed stack frames. In a method-centered view, an arc is shown between a node representing stack frames of a selected method and a node representing adjacent stack frames. The graph can be based on call stacks of all tasks or all threads, or based on call stacks of tasks or threads flagged by a user. Stack frame, thread, and/or task details are also displayed.