Digital games were reviewed as an emerging tool in educational technology. Factors such as instructional effectiveness, time on task, relationship to curricula, student socio-economic status, violence in games, and game mechanics were considered. Despite considerable variability among studies, larger overall effect sizes for the impact of games on learning were found for digital games than for early computer-assisted instruction. The review found that digital games are becoming ubiquitous, people learn from them, and transfer from games to new tasks is more closely keyed to underlying cognitive processes than superficial similarities. However, effective procedures for designing games that produce targeted instructional objectives while retaining their entertainment value remain elusive. The review also determined that time spent playing digital games should be accounted for in assessments because of their ability to capture and hold learners' attention. Finally, the effectiveness of games in providing instruction for hard-to-reach students may be an especially rewarding line of research and development.