"Additive manufacturing (AM)--commonly referred to as 'three-dimensional' or '3D' printing--is a prospective game changer with implications and opportunities that affect not just the Department of Defense (DOD) but the economy as a whole. The technology allows the 'art to part' fabrication of complex objects from a computer model without part-specific tooling or human intervention. AM has already impacted a variety of industries and has the potential to present legal and economic issues with its strong economic and health-care benefits. Because of its remarkable ability to produce a wide variety of objects, AM also can have significant national security implications. The purpose of this paper is to provide a general introduction to these issues for nontechnical readers through a survey of the recent history and the current state of technology. Included in this paper is a brief review identifying key individuals and organizations shaping developments as well as projected trends. AM refers to the production of a three-dimensional object through the layer-by-layer addition of material according to a geometrical computer model. AM contrasts with other forms of manufacturing that require either the removal or alteration of material to produce a completed object. [...] The propagation of this technology has generated a host of national security considerations, which connect to broader economic and policy developments."