Due to the opening up of public transport to competition in Île-de-France, the Marne et Seine bus network will be created on 1 August 2023, corresponding to public service delegation number 21 established by Île-de-France Mobilités.

A call for tenders was therefore launched by the organizing authority in order to designate a company that will operate the network for a period of eight years.

[1] The network consisted of SITUS ex-routes 2, 7, 8, 10, 21, 22, 41, 42, 51, 71, 81 and 82 while operated by CEA Transports, lines 1, 3, 4, 5, 6, 9 of SITUS and route 12 of Arlequin operated by Transdev SETRA, plus the routes B, J1, J2, K, O1, O2 and U of Transdev STRAV.

[2] On January 1, 2024 and following the end of the outgoing contract, the Express 100 Torcy-Créteil route is taken over by Transdev Coteaux de la Marne.

As of April 8, 2024, the Marne et Seine network will apply the new single regional numbering principle planned by Île-de-France Mobilités, removing duplicates and letters.