Pre-treatment is a key step in the production of bioethanol from lignocellulosic biomass. Current pre-treatment techniques including physical, chemical and physico-chemical methods may increase the cost of production and produce inhibitors. In addition, they are not environmentally friendly. On the other hand, biological pre-treatment is mild, less costly, eco-friendly and consumes less energy. Despite all these benefits, several factors affect the biological pre-treatment process including microbial strain, the culture and environmental conditions as well as the type of lignocellulose material. To overcome these setbacks, different forms of biological pre-treatments such as microbial and ligninolytic enzyme pre-treatments as well as processes are studied. This review presents an overview of different forms of biological pre-treatment, various processes carried out with the aim of enhancing delignification and drawbacks of this pre-treatment process.