Additive manufacturing (AM) is attractive for producing parts with access to unprecedented geometry/configuration complexity, material composition gradient control, and lightweight structure design not attainable by traditional processes. However, the long-term success of this rapidly developing technology hinges, to a large degree, on the ability to produce functional parts and components reliably. Controlling defects is of primary importance to attain AM metal parts with mechanical strength and fatigue life approaching their forged counterparts. Defects in AM parts fall into two main categories: porosity and crack. These can be incurred by various mechanisms: lack of fusion, keyhole collapse, gas porosity, balling, solidification cracking, solid-state cracking, and surface-connected porosity. Defects can also result from entrapment of impurities. Defects arise from the interplay between feedstock and AM beam energy, which involves complex, transient thermophysical and chemical processes (Scheme 1). As such, defects can be feedstock-, equipment-, and processes-related. Consequently, defect reduction starts with the quality control of feedstocks.