Lignin is a highly cross-linked aromatic heteropolymer. As it is one of the most abundant carbon reservoirs in the environment, its decomposition plays a key role in the global carbon cycle and biomass utilization. However, lignin degradation remains highly challenge, due to its inherent heterogeneity and recalcitrant chemical structure. Microorganisms from different environments have been found to have the capacities of lignin degradation. Moreover, a variety of oxidoreductases in these microorganisms have been identified to be involved in lignin degradation. However, the lignin degradation mechanisms are not yet well-studied. Thus, exploring the lignin-degrading enzyme system and metabolic network are critical to studying the mechanism of microbial metabolism of lignin. This article reviews the ligninolytic enzymes, including their components and extracellular secretion mechanism, as well as the lignin biodegradation pathways. Moreover, it provides clues to further explore mechanisms of lignin biodegradation and strategies of sustainable biomass utilization.