relion (for REgularised LIkelihood OptimisatioN, pronounce rely-on) is a software package that employs an empirical Bayesian approach for electron cryo-microscopy (cryo-EM) structure determination. It is developed in the group of Sjors Scheres at the MRC Laboratory of Molecular Biology.


As the cryo-EM resolution revolution progresses, software protectionism is also on the rise. We are proud to distribute relion under a GPLv2 license. This means that anyone (including commercial users) can download, use and modify relion for free. If relion is useful in your work, please do make sure that our Team members are credited appropriately and cite our papers.

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These pages refer to RELION-5.0, which is now in public beta-testing. For documentation on the latest stable release of RELION-4.0, please see here.