  A key process within astronomy is the exchange of mass, momentum, and energy
between diffuse plasmas in many types of astronomical sources (including
planetary nebulae, wind-blown bubbles, supernova remnants, starburst
superwinds, and the intracluster medium) and dense, embedded clouds or clumps.
This transfer affects the large scale flows of the diffuse plasmas as well as
the evolution of the clumps. I review our current understanding of
mass-injection processes, and examine intermediate-scale structure and the
global effect of mass-loading on a flow. I then discuss mass-loading in a
variety of diffuse sources.
