The Mid-Appalachian Region (MAR) of the National Speleological Society (NSS) is a regional organization of the NSS consisting of various grottos and organized caving clubs within the general geographic area, or region, of Pennsylvania, Maryland, Delaware, and New Jersey.

The MAR, an internal organization of the NSS, is dedicated to the principles of the NSS, to promote fellowship among its members, and to advance the science of speleology.

The Mid-Appalachian Region of the NSS was officially established on October 10, 1953 at Shippensburg State Teachers College, currently known as Shippensburg University, in Shippensburg, Pennsylvania.

It sponsors two regional field meets (Spring and Fall), and hosts its annual business meeting in the month of February. The region publishes a newsletter, the "MAR Breakdown", which is published three times a year and occasionally publishes county bulletins on Pennsylvania caves.