The Chicago and Milwaukee Subdivision is a 85.5-mile (137.6 km) railway line running between Chicago, Illinois and Milwaukee, Wisconsin. It is mostly dispatched by Canadian Pacific Kansas City Limited from a CP Rail facility in Minneapolis. From Pacific Junction to Chicago Union Station, it is dispatched by Metra's Consolidated Control Facility. The C&M Subdivision is the primary of CPKC's two northern routes from Chicago. The Union Pacific Railroad operates its Milwaukee Subdivision, a former Chicago & Northwestern Railway line, parallel to the C&M.

Chicago Union Station is an intercity and commuter rail terminal located in the West Loop neighborhood of the Near West Side of Chicago. Amtrak's flagship station in the Midwest, Union Station is the terminus of eight national long-distance routes and seven regional corridor routes. Six Metra commuter lines also terminate here.