As amateur radio operators we experience propagation of RF energy first hand.  At times this propagation may seem mysterious and strange, however, it can be modeled by our current physical understanding of electromagnetics.  This allows us to make some predictions about how propagation will unfold.  Our understanding falters when RF energy propagates in environments that are far to complex to contain within the best models we can build.  This is when the mystery returns.  This talk will explore our physical understanding of propagation, what factors govern it, and how it interacts with the environment and ionosphere.  Amateur radio operators can, using this understanding, make better choices for more efficient RF propagation.