Longfellow, Alden & Harlow was a Boston and Pittsburgh-based architecture firm founded in 1886 by Alexander Wadsworth Longfellow, Jr. and Alfred Branch Harlow. In 1887 Frank Ellis Alden joined the firm as a partner. Both Longfellow and Alden had previously worked in the Boston office of H. H. Richardson and Harlow worked for McKim, Mead & White. The firm was active in both Boston and Pittsburgh until 1896 when the partnership dissolved; A.W. Longfellow, Jr. continued his practice in Boston and Alden & Harlow formed their own firm in Pittsburgh.