Biomethanation is a process that converts biomass, organic waste or syngas into biogas which can be further upgraded into natural gas grid biomethane via either conventional upgrading techniques such as pressure swing adsorption (PSA), chemical solvent scrubbing (using amines), and pressurized water scrubbing or biological methods such as in-situ, ex-situ or hybrid Biomethanation process. Biological process of biomethanation has gained popularity due to less environmental impacts and more economic benefits than the conventional techniques. Enriched biomethane produced from biological biomethanation contributes as renewable fuel. Several pilot scale and full-scale ex-situ biomethanation techniques have been implemented in recent years. However, In-situ and syngas biomethanation need more attention as these processes can bring more benefits using wide range of biomass and less equipment. This review will provide comprehensive overview of the current state, challenges, and prospects of biological biomethanation. This thesis presents the most recent case studies and the intra and inter comparative analysis of in-situ, ex-situ and syngas biomethanation to figure out the most suitable reactor type for scaling up with highest methane content. However, reviewing biotic and abiotic factors address the prospects and potentiality of using Trickle bed reactors, utilizing direct electron transfer (DIET) and carrier materials to maximize the output. Compared to in-situ biomethanation, ex-situ biomethanation has made more progress in scaling up successfully, and it can achieve high methane purity (around 95-99%) with Trickle bed reactors. In-situ biomethanation has difficulties due to poor gas-liquid transfer rate, process instability and microbial inhibition by high hydrogen partial pressure. These can be overcome by using carrier materials, applying DIET, optimizing operational conditions by controlling biotic and abiotic factors. Methanobacter was found to be more common in biomethanation and sometimes they show better performance with synergistic culture with other bacteria.