Despite the growing importance of crowdsourcing activities, little is known about the influence of intrapersonal characteristics of external actors on the outcome for the involved firms. This study therefore explores how interests, abilities, and motivation explain contribution behavior of individuals in idea contests. Analyzing a data set that combines survey data and server log file information of 33 idea contests hosted by the platform operator Atizo, we find that the breadth of individuals’ interest is positively related to the number of submitted solution ideas. Furthermore, we observe a positive interaction effect between enjoyment and professional experience on contribution behavior. According to these findings, the most valuable external actors identified in this study combine high levels of motivation with abilities and have a wide range of interests. Our study contributes to existing research and is useful for firms and platform managers that are involved in crowdsourcing activities.