This full volume article is the third in a series of articles that cover several “standard” American box car designs that were built in large quantities during the first half of the 20th Century. In this article, Pat Wider covers the 1923-29 design A.R.A. single-sheathed and double-sheathed, standard steel frame box cars as well as the A.R.A. “proposed-standard” all-steel box cars that were built from 1924 to 1934 following several American Railroad Administration designs. These cars were the immediate predecessors of the A.R.A. Standard Box Car of 1932. The standard single- and double-sheathed steel frame box cars were built for or owned by many railroads including the A&WP, AT&SF, BAR, B&M, C&O, CGW, CRI&P, GA, GF&A, L&N, M&StL, SAL, SP, UP, WAG, and WofA. The A.R.A. “proposed-standard” all-steel box cars were built for or owned by the B&O, B&M, C&O, CGW, CRRofNJ, DT&I, Erie, L&NE, MEC, MTC, NKP, NYC, PM, PRR, and W&LE. The article includes 151 black & white and color photographs, 35 diagrams, and 3 tables. Due to the extensive scope of the subject, the Pennsy’s X29 A.R.A. all-steel box cars will be the subject of a following article in a future volume of Railway Prototype Cyclopedia.