Reykjanesbær is a municipality on the Southern Peninsula in Iceland, though the name is also used by locals to refer to the suburban region of Keflavík and Njarðvík which have grown together over the years. The municipality is made up of the towns Keflavík, Njarðvík and the village of Hafnir. The municipality was created in 1994 when the inhabitants of the three towns voted to merge them into one. Reykjanesbær is the fifth largest municipality in Iceland, with 18,920 citizens (2019).

Of the three towns which make up the municipality, Keflavík is the largest, while Hafnir is the smallest and some 10 kilometers distant. Keflavík and Njarðvík were originally distinct towns but gradually grew together over the course of the latter half of the 20th century, until the only thing separating them was a single street. The northern side of the street belonged to Keflavík and the southern side to Njarðvík. Since May 2009 the township of Njarðvík has been the location of the Viking World museum.

In 2006, when the United States Navy closed Naval Air Station Keflavík, the site was taken over by the development agency Kadeco, and renamed Ásbrú. A university, Keilir, was founded and now Ásbrú houses the campuses of various educational institutions and also businesses, both newly founded and relocated to the site of the air base.