Additive manufacturing (AM), or 3D printing, is an emerging technology that “adds” materials up and constructs products through a layer-by-layer procedure. Laser powder bed fusion (LPBF) is a powder-bed-based AM technology that can fabricate a large variety of metallic materials with excellent quality and accuracy. However, various defects such as porosity, cracks, and incursions can be generated during the printing process. As the most universal and a near-inevitable defect, porosity plays a substantial role in determining the mechanical performance of as-printed products. This work presents a comprehensive review of literatures that focused on the porosity in LPBF printed metals. The formation mechanisms, evaluation methods, effects on mechanical performance with corresponding models, and controlling methods of porosity have been illustrated and discussed in-depth. Achievements in four representative metals, namely Ti?6Al?4V, 316L, Inconel 718, and AlSi10Mg, have been critically reviewed with a statistical analysis on the correlation between porosity fraction and tensile properties. Ductility has been determined as the most sensitive property to porosity among several key tensile properties. This review also provides potential directions and opportunities to address the current porosity-related challenges.Additive manufacturing (AM), or 3D printing, is an emerging technology that “adds” materials up and constructs products through a layer-by-layer procedure. Laser powder bed fusion (LPBF) is a powder-bed-based AM technology that can fabricate a large variety of metallic materials with excellent quality and accuracy. However, various defects such as porosity, cracks, and incursions can be generated during the printing process. As the most universal and a near-inevitable defect, porosity plays a substantial role in determining the mechanical performance of as-printed products. This work presents a comprehensive review of literatures that focused on the porosity in LPBF printed metals. The formation mechanisms, evaluation methods, effects on mechanical performance with corresponding models, and controlling methods of porosity have been illustrated and discussed in-depth. Achievements in four representative metals, namely Ti?6Al?4V, 316L, Inconel 718, and AlSi10Mg, have been critically reviewed with a statistical analysis on the correlation between porosity fraction and tensile properties. Ductility has been determined as the most sensitive property to porosity among several key tensile properties. This review also provides potential directions and opportunities to address the current porosity-related challenges.