Interstate 97 is the country's only intra-county mainline Interstate highway. At less than 18 miles in length, it is currently the second-shortest mainline Interstate pending any extensions of the southern iteration of Interstate 87. I-97 was conceived as an Interstate corridor linking the areas of Maryland's largest city, Baltimore, and its capital, Annapolis. Situated in Anne Arundel County, it runs between the U.S. Route 50/301 John Hanson Highway, which is also secretly Interstate 595, in Parole (outside of Annapolis) and Interstate 695, the Baltimore Beltway, in Ferndale, at which point it ties into an approach road to Interstate 895 and the Baltimore Harbor Tunnel. I-97 provides access to the Baltimore/Washington International Airport and, via US 50/301, the Chesapeake Bay Bridge.

I-97 physically has the appearance of two separate highways. From its south end to its interchange with Maryland routes 3 and 32 in Millersville it is two lanes in each direction, with little development surrounding it. At Millerville, I-97 shifts nearly due north and widens to six lanes, a configuration it maintains through more suburban territory to I-695. I-97 from Millersville northward directly replaced a previous segment of MD 3 which was built in the 1950s as the Glen Burnie Bypass in tandem with the Harbor Tunnel Thruway; when I-97 was brought into service in the early 1990s, the bypass was upgraded to Interstate standards, with each carriageway being widened and paved over with concrete and all interchanges being reconfigured. From US 50/301 to Crownsville, I-97 functionally replaced Maryland Route 178 and was built as a new roadway, while from there to Millersville it absorbed what had been the easternmost two miles of MD 32. I-97 from I-695 southward to MD 3/32 forms part of an alternate corridor to Interstate 95 between Baltimore and Richmond, Virginia along with the entire present course of MD 3 as well as US 301 through Southern Maryland and across the Potomac River to Virginia's Northern Neck.