The U.S. Post Office—Waltham Main is a historic post office building at 774 Main Street in Waltham, Massachusetts. The T-shaped brick and stone building was built in 1935, as part of a Works Progress Administration project during the Great Depression. The Classical Revival building was designed by the Boston firm of Wadsworth, Hubbard and Smith. The interior is of a layout typical of other period post offices, with a central lobby area flanked by the postmaster's office on the left and a work area on the right. This public area is faced in a variety of stone products, predominantly marble from a variety of sources.The building was listed on the National Register of Historic Places in 1986.