The analysis of normal and shear stresses in a cantilever beam bent by a transverse force is presented. The stress function is introduced and the governing Poisson-type partial differential equation and the accompanying boundary conditions are derived for simply and multiply connected cross sections of a prismatic beam. The exact solution to the boundary value problem is presented for circular, semi-circular, hollow-circular, elliptical, and rectangular cross sections. Approximate, but sufficiently accurate, formulas for shear stresses in thin-walled open and thin-walled closed cross sections, including multicell cross sections, are derived and applied to different profiles of interest in structural engineering. The determination of the shear center of thin-walled profiles, which is the point through which the transverse load must pass in order to have bending without torsion, is discussed in detail. The sectorial coordinate is introduced and conveniently used in this analysis. The formulas are derived with respect to the principal and non-principal centroidal axes of the cross section.