To efficiently deconstruct recalcitrant plant biomass to fermentable sugars in industrial processes, biocatalysts of higher performance and lower cost are required. The genetic diversity found in the metagenomes of natural microbial biomass decay communities may harbor such enzymes. The aim of this chapter is to describe strategies, based on metagenomic approaches, for the discovery of glycoside hydrolases (GHases) from microbial biomass decay communities, especially those from unknown or never-been-cultivated microorganisms.