The future energy system demands for a higher flexibility and higher versatility of energy carriers and conversion methods to incorporate the growing amount of renewable electricity generation methods. Renewable chemical energy carriers such as hydrogen, bio- or synthetic methane as well as further synthetic hydrocarbons have limited application nowadays, but they will most likely play an increasingly important role in the future. In this context, power-to-gas (PtG) conversion routes will be crucial for the provision of gaseous synthetic energy carriers. A power-to-gas (PtG) approach based on methanation presents a possible option to couple electricity, gas, and heat distribution networks. Integrating the respective conversion and storage technologies allows to offset fluctuations within these interconnected grids. In this context, in the chapter, the fundamentals of the methanation reaction system, the thermodynamic limitations, applied catalysts, and reactor types will be highlighted.