Mark stack overflow list. A method may be practiced in a computing environment including application code that implements garbage collection functionality. The garbage collection functionality includes pushing object references onto a mark stack, such that objects referenced on the mark stack can be marked so as to prevent memory for the objects from being recycled for use with other objects instances. The method includes acts for handling overflows of a mark stack. The method includes accessing a reference to an object. The object is processed by attempting to enumerate references to other objects from the object onto a mark stack. An overflow condition of the mark stack is detected for a referenced other object. A reference to the referenced other object is placed on an overflow list. References from the overflow list are processed.