Selenginsk (; , Selengyn, , Selenge) is an urban locality (an urban-type settlement) in Kabansky District of the Republic of Buryatia, Russia, located at the head of the Selenga River delta about from Lake Baikal and about northwest of Ulan-Ude, the capital of the republic. As of the 2010 Census, its population was 14,546.
Within the framework of administrative divisions, the urban-type settlement (inhabited locality) of Selenginsk is incorporated within Kabansky District as Selenginsk Urban-Type Settlement (an administrative division of the district). As a municipal division, Selenginsk Urban-Type Settlement is incorporated within Kabansky Municipal District as Selenginskoye Urban Settlement.
Selenginsk stands on the Trans-Siberian Railway and the Trans-Siberian Highway.