During the early 1800s, Maryland's first industries centered around the Baltimore shipyards. Small ironworks cast parts for sailing vessels, and many laborers worked as shipbuilders. By the 1850s, Baltimore was also producing weather-measuring instruments and fertilizers, and by the 1930s, it was a major center of metal refining. The city remains an important manufacturer of automobiles and parts, steel, and instruments. Manufacturing is led by the printing and publishing industry, the food industry, the machinery industry, and the chemical industry.

Value of shipments by manufacturers in 1997 was $38 billion. About one-third of all manufacturing activity (by value) takes place in the city of Baltimore, followed by Baltimore County, Montgomery County, and Prince George's County. Maryland is the headquarters for six Fortune 500 companies: Lockheed Martin, Marriott International, Black and Decker, Giant Food, USF&G, and BG&E. Other major employers as of the year 2000 included ARINC, Bethlehem Steel, Computer Sciences Corp., General Motors, McCormick and Co., Northrop Grumman, and Perdue Farms, Inc.

Earnings of persons employed in Maryland increased from $95.2 billion in 1997 to $101.4 billion in 1998, an increase of 6.5%. The largest industries in 1998 were services, 33.0% of earnings; state and local government, 10.9%; and retail trade, 9.5%. Of the industries that accounted for at least 5% of earnings in 1998, the slowest growing from 1997 to 1998 was state and local government, which increased 2.3%; the fastest was finance, insurance, and real estate (8.1% of earnings in 1998), which increased 9.7%.