Digestibility is the result of the interaction between a feed and an animal. The high cost of in vivo measurements of energy and nutrients digestibility make it useful to predict it from characteristics of the feed: for example energy is often calculated from chemical composition, while for some feedstuffs physical properties (color, texture) can provide an indication on nutrient digestibility. Near Infrared spectroscopy (NIRS) is an analytical technique based on the absorption of light by samples. As NIRS is cheap and rapid it is widely used to predict chemical composition of food/feed samples. The use of NIRS for the prediction of digestibility is less easy as it requires a large number of reference data. In some contexts NIRS has been shown to supply valuable information on energy value of feeds, or digestibility of raw materials. A part of the information on the digestion process can be found in feces, because feces contain non-digested feed components. NIRS can be used to characterize not only the composition of feces but also digestibility parameters. On step forward on the description and understanding of digestibility is to combine the information of feeds and feces. Experiments with NIRS showed that these two elements provide complementary information and that their combination increases the precision of prediction models. This approach can help for large scale digestibility studies. It could also be applied to on farm monitoring of digestibility.