Selecting new product or service ideas that are worthwhile to be exploited has always been a major challenge to firms of all kinds. Recent developments, however, add a new facet to the evaluation challenge. Initiatives such as innovation contests, in which interested users may submit their ideas or solutions to firm relevant problems, frequently lead to several tens of thousands of submissions. Consequently, solutions are needed that help identifying the most promising ideas. The book "Open Evaluation" proposes a potential solution: integrating external stakeholders into the assessment of product and service ideas by means of IT, i.e. open evaluation. Based on both qualitative and quantitative research, the author examines design options, strategies, and the capacity of open evaluation to efficiently and effectively support decision-making for innovation.