Biorefinery concept is an attractive concept in producing biofuels or bioenergy from biomass. It emphasizes the production of various products from biomass in a sustainable and environmentally friendly manner. However, the major hindrance for realizing biorefinery at the commercial scale is the high cost of enzymes used for the bioconversion of biomass into fermentable sugars. Therefore, on-site enzyme production which offers a better process economic is proposed as an alternative to the commercial enzyme application. Furthermore, the production of single-cell protein as a side product could generate more income to the biorefinery. This chapter overviewed the most relevant enzymes from a biorefinery context and the current trends and strategies to improve enzyme production. In addition, the underlying concept of single-cell protein, including potential substrates and microorganisms, is also discussed. The aim is to further improve on the production yields as well as process economics so that enzymes and single-cell protein could become value-added products in the integrated biorefineries.