In recent times, the escalation of greenhouse gases, air pollution and depletion of the ozone layer has enforced the researchers to renovate the regular use of fossil fuels into alternate methods which are non-toxic, eco-friendly, and cost-effective. Biomass is one of the traditions to swap fossil fuels. Biomass can be transmogrified into beneficial and eco-friendly forms of energy under various conversion processes. The obtained energy can be used for heating water, industrial heating process, and generating electricity. Pyrolysis is a method to alter biomass into useful products, as the final yields of this process include bio-oil, char, methane (CH4), hydrogen (H2), carbon monoxide (CO) and carbon dioxide (CO2). It is well known for its high efficiency and environmental performance. In this method even the agricultural residues, waste woods, solid municipal waste, plant wastes can be utilized. This review comprehends the various concepts on products of biomass pyrolysis, mechanisms, and several pre-treatment processes used for efficient pyrolysis of biomass have been analysed. The impact of various fundamental constraints such as temperature, heating rate, particle size was studied and their influence on yield and composition were studied.