The Maryland and Delaware Railroad Company is a Class III short-line railroad, formed in 1977 to operate several branch lines of the former Penn Central Railroad in both Maryland and Delaware, United States. These branches were omitted from the system plan for Conrail in 1976 and would have been discontinued without state subsidies. As an alternative to the higher cost of subsidizing Conrail as the operator of the branch lines, the Maryland and Delaware governments selected the Maryland and Delaware Railroad Company (MDDE) to serve as the designated operator.

Railroad classes are the system by which freight railroads are designated in the United States. Railroads are assigned to Class I, II or III according to annual revenue criteria originally set by the Surface Transportation Board in 1992. With annual adjustments for inflation, the 2019 thresholds were US$504,803,294 for Class I carriers and US$40,384,263 for Class II carriers.