The JRockit Mission Control Memory Leak Detector, or Memleak for short, is a dynamic tool that can be attached to a running JRockit instance. Memleak can be used to track how heap memory usage in the Java runtime changes over time for each type (class) in the system. It can also find out which types have instances pointing to a certain other type, or to find out which instances are referring a certain other instance. Allocation tracing can be enabled to track allocations of a certain type of object. This all sounds complicated, but it is actually quite easy to use and supported by a rich graphical user interface. Before we show how to use it to resolve memory leaks, we need to discuss some of the architectural consequences of how Memleak is designed.