The object of the present review is to analyze the methodologies that are commonly used to estimate protein degradability in the rumen, focusing on their attributes and limitations to offer suggestions for improving their use. This information is essential for selecting food types when formulating feed diets. A reliable prediction of the digestibility of ruminal proteins is basic information necessary for optimizing the use of nitrogenous sources because digestibility can translate, on the one hand, into higher yields of milk, milk protein, meat or wool and, on the other hand, into lower excretion of nitrogenous compounds into the environment; it also has an impact on animal health and welfare. Traditionally, the digestibility of feed proteins in the rumen has been predicted by in vivo, in situ and in vitro methods, but other techniques based on infrared spectroscopy have been developed, notably the NIRS and FTIR methods. All of these techniques present limitations, such as a disturbance factor or a source of error, that may result in inaccurate predictions. The in situ and in vitro methods, which use enzyme extracts of ruminal origin, and FTIR probably have the greatest advantages, but they need to be perfected through further research.