This chapter is concerned with the dynamics of wave-mean flow interaction in the context of two phenomena, mean meridional overturning circulation and stratospheric sudden warming. We will examine the former in both Eulerian and Lagrangian senses. Those observed time-zonal mean structures in the troposphere are first examined in Sections 10.1 and 10.2 respectively. A linear theory for the two aspects of this phenomenon is discussed in Section 10.3. The concepts of residual circulation, Eliassen–Palm vector and transformed Eulerian mean (TEM) equations are elaborated in Section 10.3.1. In Section 10.3.2, we present the annual mean distributions of eddy forcing, diabatic forcing and frictional forcing deduced from five years of global data. They are used in this formalism to determine the corresponding annual mean residual circulation in Section 10.3.3. The results reveal the characteristics of such overturning circulation and its extent of agreement with observation. The results also bring to light the relative importance of the several mechanisms in different latitudes responsible for the overturning circulation. The counterpart analyses of the seasonal mean residual circulations are discussed in Section 10.3.4. Section 10.4 discusses the Non-Acceleration Theorem that has a direct bearing on our interpretation of stratospheric sudden warming. In Section 10.5, we discuss the dynamics of such a dramatic transient phenomenon with a model formulation and illustrate it with the results of a seminal study.