Understanding the characteristics of the large-scale circulation and climate requires both the analysis of observational data and interpretation of the physical and dynamical processes involved through theoretical analysis and modeling. In the following sections the spatio-temporal characteristics of the circulation in extratropical and tropical latitudes are discussed, together with consideration of their interactions. In section 3.2 the focus of general circulation transport mechanisms was on zonal mean flow, meridional standing cells, and time and space eddies. The alternative paradigm, implicit in the classical work of Rossby, Namias, Palmén, and Riehl, among others, is that the high and low-frequency transient components can be separated from the time mean (zonal mean and stationary wave) components. Wallace (1987) points out that low-frequency dynamics, including important longitudinally dependent interactions between the time-mean flow and transients, began to receive attention in the late 1970s. This chapter examines the outcomes of the extensive work that has been performed. The discussion begins with an account of the westerly vortex and jetstreams, followed by consideration of planetary waves, zonal and blocked flows, and low-frequency variability and persistence.