This chapter offers an overview of lithospheric rheology as demonstrated by laboratory measurements of rock deformation, theoretical modeling of lithosphere elasticity, rigidity and flexure, seismic observations on the depth distribution of crustal and upper mantle seismicity, and models of upper mantle viscosity as constrained by field observations of postglacial rebound. Several excellent comprehensive monographs have been published recently on a number of these topics, including overviews of lithosphere rheology (Ranalli, 1995), deformation (Karato, 2008), flexure and isostasy (Watts, 2001). The reader is advised to consult these monographs for complete synopses of the methods, their geophysical applications and results, while this chapter provides only a general overview of the topics illustrated by recent research achievements in the field. The structure of this chapter follows the pattern of the other chapters: first, the basic parameters related to lithosphere rheology are introduced and discussed based on laboratory data; next, the theoretical background is briefly introduced with focus on model assumptions, limitations, and uncertainties; finally, the major research results are presented for different oceanic and continental tectonic settings and discussed within the global framework of lithosphere structure and evolution.