Combinatorial Theory is a peer-reviewed diamond open access mathematical journal specializing in the field of combinatorics.

It was established in 2021, when the vast majority of the editorial board of the Elsevier-published Journal of Combinatorial Theory, Series A left to create a new journal.

[1][2] The journal operates on a diamond open access model, in which publication costs are underwritten by voluntary contributions from universities, foundations, and other organizations.

Authors do not pay submission fees or article processing charges, and the journal belongs to the Free Journal Network.

[3] All content is published under a Creative Commons license.