Wire arc additive manufacturing (WAAM) is one of the most relevant additive manufacturing technologies that uses an electric arc to melt and deposit material in wire form, layer by layer, to create three-dimensional objects. WAAM technology is considered a metal additive manufacturing (MAM) process that has gained popularity in various industrial sectors, due to its ability to manufacture large metal parts and elements with high speed and low cost compared to other additive manufacturing techniques. One of the main applications of WAAM is in the aerospace industry, where it is used to manufacture larger and high-strength alloy components, such as aircraft structural parts, aircraft turbines, and rocket engine components. Another important application of WAAM is in the manufacture of energy components, including the production of parts for electric power generation and transmission, as well as for renewable energy production. WAAM is used to manufacture components such as turbine rotors, heat exchangers, and nuclear reactor parts. In addition, other applications of WAAM include component manufacturing for the automotive industry, shipbuilding, industrial machinery, and mold and die manufacturing. However, despite the numerous applications of WAAM, significant challenges and some limitations associated with its use based on metallurgical nature of the metals and cooling processes. These limitations may result in the occurrence of defects as porosity of residual stresses. In this study, a bibliographic review of the main research lines about WAAM technology has been carried out, to stablish the state of the art of this MAM technique. The technological principles of WAAM, materials, parameters, and applications are some of the main topics that will be described in this book chapter. In addition, a comparative study has been performed to evaluate the functional performance of WAAM against others MAM processes.