This paper describes the formulation and application of a comprehensive heat flow model of the continuous casting process for steel slabs, focusing on phenomena in the mold region. The model includes a I-D transient finite-difference calculation of heat conduction within the solidifying steel shell coupled with 2-D steady-state heat conduction within the mold wall. The model features a detailed treatment of the interfacial gap between the shell and mold, including mass and momentum balances on the solid and liquid powder layers. The model predicts the solidified shell thickness down the mold, temperature in the mold and shell, thickness of the resolidified and liquid powder layers, heat flux distribution down the mold, mold water temperature rise, ideal taper of the mold walls, and other related phenomena. The important effect of non-uniform distribution of superheat is incorporated using the results from previous 3-D turbulent fluid flow calculations within the liquid cavity. The effects of oscillation mark shape and mold curvature on heat transfer and the powder layers are also included. The FORTRAN program, CONID, has a user-friendly interface and executes in less than a minute on a personal computer. Calibration of the model with experimental measurements on an operating slab caster is presented along with several example applications.