The first stamp dealing Apfelbaum was Maurice Apfelbaum who listed his occupation in the 1910 US census as "Stamp Dealer." He began dealing when his son Earl was only four years old, and by the time Earl was ten, he had begun collecting stamps and was going around to dealer shops and bourses with his father. Stamp collecting was different one hundred years ago than it is today. Most stamp business was done at bourses or in dealer shops, that is face to face, and little stamp business existed outside of major urban centers. Collectors in the country saved up for their annual visits to New York, Chicago, or Philadelphia where they would go to the many stamp shops there and purchase a years' worth of collectibles. Earl and his father continued dealing throughout the teens and twenties, but it was not yet a full time business; rather they dealt their duplicates and did a little trading as so many collectors did in those days to offset their stamp collecting habit.
The Apfelbaums became full time stamp dealers in 1930. The Great Depression killed off many businesses (as it did the Apfelbaum tailoring business), but it was kind to the stamp collecting hobby. Even workers who had lost their jobs could afford a few pennies to add some stamps to their albums, and thousands of collectors tried to become stamp dealers when they lost their day jobs. Earl was an anomaly in the Depression—he was successful, opening a succession of shops in downtown Philadelphia and running Mail Sales and Public Auctions. The stamp business was still largely face to face, and throughout the 1930s, Earl would drive his car monthly through the counties surrounding Philadelphia to display his wares, sort of as an itinerant stamp salesman. Earl's father and partner, Maurice, died when Earl was 30 in 1936.

The World War II era was good to the stamp business. The war effort made for full employment, overtime made for fat paychecks, and rationing meant that there was little (except stamps) for people to buy; so business was good. The Apfelbaum firm began to run regular monthly Public Auctions, and Earl still traveled a lot but now more to acquire philatelic material than to sell it. In the early 1950s, Earl's son Martin joined the business after a stint in the service during the Korean war. Marty's responsibilities included revamping the retail division of the company which he did by eliminating selling stamps to collectors from stock books, where a one on one relationship between the seller and buyer was necessary. He instituted the Self Service Stamp Shop where thousands of individually priced stamps and sets rested in counter books that could be browsed through by collectors. The Self Service Stamp Shop was so successful that it billed itself as the "Grand Central Station of Philately" and attracted hundreds of visitors each week. Marty was responsible for establishing the Mail Sale business where stamps of a more moderate price point than those sold at Public Auction were offered in the popular competitive bid process. The company increased its advertising and its presence at national philatelic exhibitions. In the mid 1960s, Earl started his Apfelbaum's Corner weekly column for Linn's Stamp News which ran for over twenty years and was the most popular feature in that magazine. By 1970, Apfelbaum was one of the largest and most respected stamp dealers in the country.
The last forty years have seen many changes in the firm and in the stamp business. As technology has changed, Apfelbaum has been in the forefront of computer and internet use bringing rapid listings, scans, and better prices that result from using the newer technologies. Under the direction of the fourth generation of philatelic Apfelbaums—John, Ken, Missy, and Susanne—the company runs over 25 Auction and Net Price Sales per year offering over $20 million dollars sales value in fine stamps and covers. As we have always done, we guarantee every collectors' complete satisfaction with every stamp that they buy from us, and we guarantee every stamp that we sell as being genuine and as described without time limit. We continue to be major buyers of stamps and stamp collections that are needed to fill our sales, and our buyers comb the country constantly looking at collections that collectors have for sale. If you are buying or selling, you will find that the Apfelbaum Family will meet your highest expectations. For one hundred years we have been satisfying tens of thousands of philatelists, and it is our goal in both buying and selling to treat you as we would wish to be treated ourselves.