Word count (Abstract): 276Word count (Main text): 8,362Abstract Reinforcement learning and decision-making (RLDM) provide a quantitative framework, which allows us to specify psychiatric conditions with basic dimensions of neurocognitive functioning. RLDM offer a novel approach to assess and potentially diagnose psychiatric patients, and there is growing enthusiasm on RLDM and Computational Psychiatry among clinical researchers. Such a framework can also provide insights into the brain substrates of particular RLDM processes as exemplified by modelbased functional magnetic resonance imaging (fMRI) or electroencephalogram (EEG).However, many researchers often find the approach too technical and have difficulty adopting it for their research. Thus, there remains a critical need to develop a userfriendly tool for the wide dissemination of computational psychiatric methods. We introduce an R package called hBayesDM (hierarchical Bayesian modeling of Decision-Making tasks), which offers computational modeling on an array of RLDM tasks and social exchange games. The hBayesDM package offers state-of-the-art hierarchical Bayesian modeling, where both individual and group parameters (i.e., posterior distributions) are estimated simultaneously in a mutually constraining fashion. At the same time, it is extremely user-friendly: users can perform computational modeling, output visualization, and Bayesian model comparisons-each with a single line of coding.Users can also extract trial-by-trial latent variables (e.g., prediction errors) required for model-based fMRI/EEG. With the hBayesDM package, we anticipate that anyone with minimal knowledge of programming can take advantage of cutting-edge computational modeling approaches and investigate the underlying processes of and interactions between multiple decision-making (e.g., goal-directed, habitual, and Pavlovian) systems.In this way, it is our expectation that the hBayesDM package will contribute to the dissemination of advanced modeling approaches and enable a wide range of researchers to easily perform computational psychiatric research within their populations.Performing computational psychiatric research, however, especially computational modeling, is a challenging task for many clinical researchers or those with limited quantitative skills. Computational modeling involves multiple steps including designing/adopting laboratory tasks, building a theoretical framework of the task with a set of assumptions and mathematical equations, formulating multiple computational models based on the assumptions, estimating model parameters of each model, and quantitatively comparing the models of interest (e.g., Busemeyer & Diederich, 2010;Wiecki et al., 2015). It is a pressing issue how to train clinical researchers in mental health (e.g., psychiatrists and clinical psychologists) so that they can receive in-depth training across several related fields including cognitive science, advanced statistics, and neuroscience (Montague et al., 2012). For the dissemination of Computational Ps...