These files accompany The Dual Mechanisms of Cognitive Control dataset: A theoretically-guided within-subject task fMRI battery by Joset A. Etzel, Rachel E. Brough, Michael C. Freund, Alexander Kizhner, Yanli Lin, Matthew F. Singh, Rongxiang Tang, Allison Tay, Anxu Wang, and Todd S. Braver. Published in [Scientific Data][1] and [preprint via bioRxiv][2]. The [DMCC55B dataset][3] is the initial release of [Dual Mechanisms of Cognitive Control (DMCC)][4] project data. The DMCC55B dataset has 55 healthy unrelated young adult participants. Each performed four well-established cognitive control tasks (Stroop, AX-CPT, Cued Task-Switching, and Sternberg Working Memory) while undergoing moderately high-resolution functional MRI scanning. The dataset includes a range of state and trait self-report questionnaires, as well as behavioural tasks assessing individual differences in cognitive ability. The DMCC project is on-going and features additional components (e.g., related participants, manipulations of cognitive control mode, resting state fMRI, longitudinal testing) that will be publicly released following study completion. This DMCC55B subset is released early with the aim of encouraging wider use and greater benefit to the scientific community. The DMCC55B dataset is suitable for benchmarking and methods exploration, as well as analyses of task performance and individual differences. [1]: https://doi.org/10.1038/s41597-022-01226-4 [2]: https://doi.org/10.1101/2021.05.28.446178 [3]: https://openneuro.org/datasets/ds003465/ [4]: https://sites.wustl.edu/dualmechanisms/