The presence of rotation introduces new parameters and constraints on fluid motions discussed in general terms before [1]. It is of interest to develop here in more detail the physical implications of these rotation effects. To those working with rotating fluids, the material presented in this paper is not new, except, perhaps, for some aspects of the section on turbulence scales. It is nevertheless useful to recall the fundamental processes. To others working in fluid mechanics but who are not so familiar with rotating fluids, the contents of this paper is a good introduction to what follows in later chapters in this volume.