Book excerpt: Published by the American Geophysical Union as part of the Geophysical Monograph Series, Volume 93. A principal goal of space plasma researchers is to understand the influence of various transport processes on each other, even when such processes operate at widely varying spatial and temporal scales. We know that large-scale plasma flows in space lead to unstable conditions with small spatial (centimeters to meters) and temporal (microseconds to seconds) scales. The large-scale flows, for example in the magnetosphere-ionosphere system, involve scale lengths of kilometers to several Earth radii and temporal scales of minutes to hours. We must know specific contextual answers to the questions: Do the small-scale waves (microprocesses) modify the large-scale flows? Do these modifications significantly affect the transport of mass, momentum, and energy? How can such coupling processes and their influences be revealed observationally? And, perhaps most challenging of all, how do we incorporate the microprocesses into theoretical models of larger-scale space plasma transport?