Larger structures in the Universe are thought to form hierarchically from the mergers of many smaller structures. Dramatic evidence for hierarchical structure formation can be seen around our own Galaxy in the form of streams and clouds of stellar debris left over from the destruction of smaller galaxies.  The properties of this debris can be broadly explained by simply considering the nature of stellar orbits around the Galaxy. In this talk I will discuss some of the implications of such simple models for the interpretation of stellar debris.