This paper shows the main factors of variation and the predicting methods for the digestibility and ingestibility of maize silage. The digestibility of maize silage is nowadays well known, having been extensively studied, especially in France. However, new investigations should be necessary on the influence of environmental conditions during the period extending from flowering to the glassy stage of the grain (which seems crucial as regards the evolution of digestibility), and also on ways of improving the accuracy of predicting cell-wall digestibility. The influence of plant characteristics on the ingestibility of the silage is much less known. There are probably significant relationships between, on the one side, maize silage ingestibility and, on the other, its digestibility and speed of degradation, as in the case with the usual forage species, but it seems difficult to set up a hierarchy of these factors without further and more thorough studies. Moreover, the validation of various equations presently available to predict the ingestibility of maize silage under practical conditions (phenotypic value) would imply the creation of new standardized methods.