Today's online news environment is increasingly characterized by personalized news selections, relying on algorithmic solutions for extracting relevant articles and composing an individual's news diet. Yet, the impact of such recommendation algorithms on how we consume and perceive news is still understudied. We therefore developed one of the first software solutions to conduct studies on effects of news recommender systems in a realistic setting. The web app of our framework (called 3bij3) displays real-time news articles selected by different mechanisms. 3bij3 can be used to conduct large-scale field experiments, in which participants' use of the site can be tracked over extended periods of time. Compared to previous work, 3bij3 gives researchers control over the recommendation system under study and creates a realistic environment for the participants. It integrates web scraping, different methods to compare and classify news articles, different recommender systems, a web interface for participants, gamification elements, and a user survey to enrich the behavioral measures obtained.Keywords: News, recommender systems, computational social science, web application 3BIJ3 FRAMEWORK FOR RECOMMENDER SYSTEMS 3 3bij3 -Developing a framework for researching recommender systems and their effects News usage online has undergone considerable changes: Increasingly, the selection and presentation of news gets adapted to each user individually (Thurman & Schifferes, 2012) using recommender systems, algorithms that decide which articles are displayed to whom based on criteria such as past behavior and/or ratings of similar users (Ricci, Rokach, & Shapira, 2011). While these systems already form an integral part of news sites and social network sites, their impact on how we consume and perceive news is still understudied. Better understanding recommender systems is imperative for practitioners and academia: Media need insights into how editorial decisions can be combined with systems accommodating their audiences' wishes, while maintaining vital functions of journalism for democracy (Bhaskar, 2016; Schlesinger & Doyle, 2015). Communication researchers need a better understanding of how recommender systems affect selective exposure, political attitudes, and knowledge.So far, the effect of algorithm-based selection on the diversity of news diets has mostly been discussed negatively, assuming that such systems limit the breadth of viewpoints and topics. However, recent studies challenge this conception by showing that, especially compared to other selection processes (e.g., by human editors), algorithms might not lead to more narrowed media diets after all (Möller, Trilling, Helberger, & van Es, 2018;Nguyen, Hui, Harper, Terveen, & Konstan, 2014). To provide researchers with a tool to contribute to this debate, this article sets out to develop one of the first research designs to tackle the issue of studying recommender systems in the context of news and political communication. We present a framework called 3bij3. 3bij3 ...