Additive manufacturing is a layer based manufacturing process aimed at producing parts directly from a 3D model. This paper provides a review of key technologies for metal additive manufacturing. It focuses on the effect of important process parameters on the microstructure and mechanical properties of the resulting part. Several materials are considered including aerospace alloys such as titanium (TiAl6V4 “UNS R56400”), aluminum (AlSi10Mg “UNS A03600”), iron-and nickel-based alloys (stainless steel 316L “UNS S31603”, Inconel 718 “UNS N07718”, and Invar 36 FeNi36 “UNS K93600”).