This is a cost-effective way of achieving advances in criminal justice technology transfers and problemsolving. NIJ spends money only on projects that achieve specified goals through superior methods (only the winner of the challenge receives money), and administrative costs are lower for these time-limited challenges compared to multi-year grants. Among the challenges that have achieved productive results are the development of a way to predict the amount and rate of change in a body-armor vest's ballistic performance due to normal daily wear and a variety of physical, chemical, and environmental factors. Another challenge that has closed is the development of innovative solutions that provide mission-critical voice communication services to public-safety responders using commercial off-the-shelf technology. A second closed challenge is the development of "disruptive" criminal justice applications that use ultra-high speed networks with the potential to change how services and information are delivered to public-safety practitioners. A third closed challenge sought ways of developing strategies for measuring the implementation costs of public-safety benefits of the Sex Offender Registration and Notification Act. Two recent new challenges call for the use of timely and innovative randomized controlled trials that address meaningful criminal justice problems and a means to increase the transparency and accessibility of criminal justice data. Visit Challenge.gov for the most up-to-date list of competitions.