Since ruminants obtain most of their energy from their symbiotic microbiota, the efficiency of feed conversion and end-product meat and milk quality in bovines is tightly linked to the dynamics and function of the rumen microbiome. In this chapter, we give an overview of the role of the microbiota in ruminal lignocellulose degradation, who is doing what, and cover the mechanisms they utilize in the decomposition of biomass. We discuss findings from studies on well-known Ruminococcus, Fibrobacter and Prevotella isolates, as well as those from poorly understood and as-yet uncultured Bacteroidetes lineages. Collectively, these approaches have revealed new mechanistic information related to the hydrolytic capacity of cellulosomes, free enzymes, outer membrane vesicles, polysaccharide utilization loci and large multi-modular enzymes, which are generating deeper insights into the intricate microbial networks that engage in ruminal fibre digestion.