This work introduces a phenomena-based model for delignification in the kraft pulping process. The solubilization of lignin is described as a set of chemical reactions representing the entire chemistry of lignin degradation as well as dissolution of the degraded lignin. For modeling, reaction mechanisms and reactions kinetics derived mainly from the literature were used. Each reaction was simulated separately and then combined for the overall degradation. The model was validated with experimental results from pine wood meal pulping under a wide range of reaction parameters. The experimental data presented a good fit with the model. With the aid of the model, the structure and the amount of wood components, in fibers and black liquor, can be determined at any pulping stage. Several engineering parameters can be computed from the detailed chemical composition of liquor and wood or chemical pulp. These include, e.g., kappa number, brightness, yield, active alkali, effective alkali, sulfidity, and higher heating value.