Silage making process can be explained very simply, it is actually very complex and dependant on many factors, such as the natural microbial population, harvesting conditions and the sugar content of the forage. Consequently, silage quality can be very variable and the only way to effectively control the fermentation process is to use an additive. Additives are natural or industrial products added in rather large quantities to the forage or grain mass. Additives control or prevent certain types of fermentation, thus reducing losses and improving silage stability. In order to assist in the fermentation process, various silage additives have been used to improve the nutrient and energy recovery in silage, often with subsequent improvements in animal performance. The purpose for applying additives to the silage is to ensure that the growth of lactic bacteria predominates during the fermentation process, producing lactic acid in quantities high enough to ensure good silage. Therefore this review is made to focus on some practical aspects of the fermentation process and the uses of some common silage additives that include microbial inoculants, enzymes, and propionic acid.