This video introduces the topic of garbage collection (GC), one of the more complex subjects in GemStone Smalltalk. There are two types of GC: (1) in a local virtual machine (the Gem), and (2) across the entire Repository (persistent objects). “Live” objects are objects that are referenced from a persistent root. “Dead” objects are those that are not referenced from a persistent root. To identify live objects, we need to start from a system-defined well-known root (AllUsers, the collection of UserProfile instances) and identify each referenced object. This process can take hours or days.