In vitro digestion (IVD) techniques can evaluate digestibility of energy and energy-yielding nutrients in feedstuffs or complete diets for pigs and other monogastric species. These techniques can mimic the conditions of the gastro-intestinal tract and may have advantages compared with in vivo models of digestion. For example, IVD analyses require less sample material and less time, and are cheaper than in vivo digestibility analyses. Therefore, IVD provides the possibility to screen many samples and support the development of feedstuff databases and rapid feed quality evaluation systems. However, one critical step for IVD analyses is rigorous validation of in vitro digestibility data using the target animal model. For pigs, considerable validation efforts have been made. Using purified enzymes, buffers, and controlled pH, a 3-step IVD model, mimicking digestion in the stomach, small intestine, and large intestine, respectively can estimate the apparent total-tract digestibility (ATTD) of energy. The impact of evaluating the ATTD of energy is clear instantly, because it relates strongly to the DE value of feedstuffs or diets. Similarly, kinetics of glucose release during in vitro digestion of starch is an excellent indicator of net portal appearance of glucose in pigs. Kinetics of fiber degradation can be characterized by in vitro fermentation models, but these models not been validated quantitatively in the pig model. Nevertheless, kinetics of both starch digestion and fiber fermentation are related to important aspects of metabolism of nutrients, gut physiology, and health. In summary, IVD techniques can be a valuable tool to describe the ATTD of energy and kinetics of starch digestion and fiber fermentation of feedstuffs in swine.