In recent years we have witnessed a shift in the innovation landscape of organizations from closed to more open models embracing solutions from the outside. Widespread use of the internet and web 2.0 technologies have made it easier for organizations to connect with their clients, service providers, and the public at large for more collaborative problem solving and innovation. Introduction of the Open Government initiative accompanied by the America Competes Reauthorization Act signaled an unprecedented commitment by the US Federal Government to stimulating more innovation and creativity in problem solving. The policy and legislation empowered agencies to open up their problem solving space beyond their regular pool of contractors in finding solutions to the nation's most complex problems. This is an exploratory study of the adoption of challenges as an organizational innovation in public sector organizations. The main objective is to understand and explain how, and under what conditions challenges are being used by federal agencies and departments as a tool to promote innovation. The organizational innovation literature provides the main theoretical foundation for this study, but does not directly address contextual aspects regarding the type of innovation and the type of organization. The guiding framework uses concepts drawn from three literature streams: organizational innovation, open innovation, and public sector innovation. Research was conducted using a qualitative case study of challenge.gov. Data was collected from multiple adopting agencies using two primary sources: interviews with challenge managers and administrators and, archival data from the challenge.gov web platform. Related documentation was used to supplement and corroborate the main data. Analysis of the platform archival data revealed four types of challenges falling along a continuum of increasing innovation. The sequence of events, activities and conditions leading to adoption and implementation were represented as a challenge adoption model. Variations among components of the model resulted in three distinct agency groupings represented as a typology of enactments characterized as inertia, application, and change. Thus challenge adoption among agencies with varying missions, operations and conditions leads to varying enactment types and different levels of change.