Robert A. Siegel started Robert A. Siegel Auction Galleries, Inc. in 1930, and the firm has been running continuous auctions since its founding. It is currently one of the largest stamp auction houses in the world, holding several record prices. The firm has handled numerous important properties, including Lilly, Honolulu Advertiser, Zoellner, Whitman and others.

For many years, the firm also maintained a retail stock, available for outright purchase. Included as part of the retail stock was an exhibition collection of inverts, a personal favorite of Mr. Siegel.