This thesis analyzes aerodynamic forces in viscous and compressible external flows. It is unique, as the force theories discussed apply to fully viscous and compressible Navier-Stokes external flows, allowing them to be readily combined with computational fluid dynamics to form a profound basis of modern aerodynamics. This thesis makes three fundamental contributions to theoretical aerodynamics, presenting: (1) a universal far-field zonal structure that determines how disturbance flow quantities decay dynamically to the state of rest at infinity; (2) a universal and exact total-force formula for steady flow and its far-field asymptotics; and (3) a general near-field theory for the detailed diagnosis of all physical constituents of aerodynamic force and moment.