A two-dimensional numerical model is given for the analysis of the coupled thermal and mechanical behavior of the solidifying shell within the mold during continuous casting of steel. The influence of different mold wall profiles on gap formation and heat flow during casting of billets is investigated. The calculated temperatures, stresses, and strains in the shell are used to estimate the risk for formation of longitudinal cracks. The effect of an initiated and growing macroscopic subsurface crack on the shell behavior is studied. The genesis of surface cracks is discussed. The calculated results are shown to be in reasonable agreement with experimental observations reported in the literature.