The origin and nature of intrinsic toroidal plasma rotation in the scrape-off-layer are theoretically investigated. We discuss and analytically estimate three mechanisms that give rise to SOL toroidal rotation: turbulent momentum transport associated with electrostatic instabilities, pressure gradients along the poloidal direction, and deviation of the plasma velocity at the sheath entrance with respect to the Bohm's value. The results of three-dimensional global fluid simulations of tokamak scrape-off-layer in a limiter configuration are shown and compared.