The purpose of this study is to investigate how designers of commercial educational mathematics game apps describe various aspects of "integration". My investigation addresses several research questions, including what integration means to designers, why they build it into games, and how they do so. Integration is a concept described in game-based learning literature as the embedding of educational content within a game's mechanics. This concept is important to study because it is what researchers have identified as the key element that enables educational games to realize their potential. That is, when the educational content and game mechanics are aligned, educational games have potential to help students learn concepts "and" enjoy doing so. To understand how designers of commercial mathematics game apps think about integration and mathematics game design, I interviewed seven different designers one-on-one virtually. I elicited responses from designers that pertain to various aspects of their work, including how they define or describe integration, why they build integration into mathematics games, and how they build it. My analyses of the designers' interview responses indicate that their perspective and understanding of integration is similar to that of mathematics education researchers. In addition, designers integrate the mathematical content and the mechanics to ensure that students engage with mathematical "concepts". They see integration as the key design feature that moves their games beyond drill and practice and enables conceptual learning. They also design features and mechanics to keep students engaged so they do not lose focus or become overly frustrated. Finally, designers were able to describe some processes involved in designing mathematics games. This process involves playtesting, simplifying mathematical ideas, and "translating" these ideas into a digital format (via a game engine or other technological tools). The process requires multiple kinds of expertise. The results suggest that designers of integrated mathematics games are aware of integration and intentionally build integration to engage students with mathematical concepts. For mathematics educators, this enables a qualitatively different kind of learning than earlier designs that engaged students only in completing digital worksheets. Video games can now play different instructional roles in the classroom. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]