The need for innovation in the manufacturing industry to meet the consumer's fast changing preference has led to additive manufacturing (AM). Additive manufacturing works around the idea of material addition for product formation instead of conventional ways of subtracting material. Due to AM being an emerging technology, many procedures and processing parameters are not standardized, as it remained challenging for industries to produce parts that are defect free. Porosity level of the end product is of interest to the manufacturers as it reveals the material properties and microstructure of the end product. It is critical to all industries to ensure that the parts fabricated with AM are structurally sound and is safe for use in different types of operation. Thus, this book will investigate the use of non-destructive testing, specifically ultrasonic testing (UT), on metallic printed specimens for flaw detection and quantification of porosity content. This book will also do a comparison of UT against other non-destructive testing methods and conclude that the best technique used for flaw characterization in metallic three-dimensional (3D) printed specimens.