A method and system for concurrent garbage collection wherein live memory objects, i.e., not garbage, can be marked while an application executes. Root information is gleaned by taking a snapshot program roots or by arranging the stack to be scanned during execution of the program. Next, a first marking act is performed using the root information while the program executes. Modifications in the memory structure that occur during the concurrent marking act are logged or accumulated by a write watch module. The application is then paused or stopped to perform a second marking act using information from the write watch module. Following the second marking act, the garbage collection may be completed using various techniques.