Apogee Software is a video game publisher based in Aalborg, Denmark. Scott Miller founded the company in his parents' home in Garland, Texas, in 1987 as Apogee Software Productions to release his game Kingdom of Kroz. In the late 1980s and early 1990s, the company popularized a distribution model where each game consists of three episodes, with the first given away free as shareware and the other two available for purchase. Duke Nukem was a major franchise created by Apogee to use this model, and Apogee published Commander Keen and Wolfenstein 3D the same way.

Apogee began using the brand name 3D Realms for its 3D games in 1994, and in 1996 rebranded the company itself to 3D Realms to focus on traditionally-published 3D titles. Duke Nukem 3D (1996) was released under this name to great success. 3D Realms largely ceased its publishing and development operations afterwards to focus on two extensively delayed games: Prey (2006), which was under development until being taken over by another studio in 2001, and Duke Nukem Forever (2011), which remained under development until 2009. The "Apogee Software" name, library, and logo were licensed to Terry Nagy in 2008, who established Apogee Software LLC to develop and publish ports and spinoffs of Apogee titles.