Additive manufacturing involves the manufacture of complex-shaped parts layer-by-layer, in an additive fashion, directly from a computer-aided design model of an object. The introduction of additive manufacturing technologies has revolutionized product design, development, and manufacturing. The fundamental advantage of these technologies lies in their ability to rapidly produce complex-shaped parts without special tools, molds, or dies, in materials ranging from polymers to metals to ceramics, including multimaterial, functionally gradient and composite combinations as well. Virtually every industry, from consumer products to aerospace, has benefited from these technologies, resulting in better, faster, and cheaper products. In this chapter we provide an overview of additive manufacturing technologies. We begin with a step-bystep description of a basic additive manufacturing process chain, followed by a useful classification of additive manufacturing technologies into categories. In the subsequent sections, additive manufacturing processes are discussed in detail within their respective categories. The emphasis is placed on process- and categoryspecific details rather than manufacturer- or machine-specific details. Since further advancements in the field are heavily dependent on an in-depth theoretical understanding of the underlying process principles, an entire section is dedicated to describe modeling efforts in additive manufacturing technologies. After introducing the technologies, various current and emerging applications of additive manufacturing technologies are discussed. The chapter ends with a discussion of future directions, which includes a few specific areas where more improvements must occur in order to attain a wider utilization of additive manufacturing technologies. © 2007 by Taylor and Francis Group, LLC.