Additive manufacturing (AM), also known as three-dimensional (3D) printing, is a relatively new manufacturing technique that has gained significant industrial interest. AM is a key low-carbon manufacturing technology incorporating net-shaping whilst avoiding complex process chains. This manufacturing technique is appealing for a variety of applications, including aerospace, oil, gas, marine, automotive, biomedical, and nuclear, due to advantages such as component design freedom, component complexity, light weighting, toolless nature, part consolidation, and decreased material waste. To overcome the performance limitations and to take advantage of the alloy design opportunities provided by AM technology, a new generation of alloys suitable for AM is needed. In addition to this, optimising process parameters and microstructure evolution during AM can lead to improved mechanical, corrosion, fatigue, irradiation, and wear properties, amongst other benefits. With a view to select the best alloys for a given application, and to identify the compositional and property gaps of existing materials, this book presents a review of AM powder alloys, the technologies to produce and process them, and the design methodologies to conceive new formulations. The requirement to make powder AM technology sustainable are reviewed.