The first 46ers were brothers Robert and George Marshall, and their guide and family friend Herbert Clark. The Marshalls thought up the idea after spending much of their childhood in the region and examining the collection of Verplanck Colvin maps owned by their father, Louis Marshall. They devised criteria for the high peaks they would climb, choosing any summit that was more than 4,000 ft (1,219 m) above sea level in elevation with at least 300 feet (91.4 m) of vertical rise on all sides and separated from the next closest summit by 0.75 mile (1.2 km). They initially planned to climb only the summits above , of which there were 42, and did so between 1918 and 1924.
They climbed the mountains later, on the suggestion of friends.
At the time that they undertook this goal, there were no trails up many of the peaks, making this a particularly formidable accomplishment. One of the peaks, Mount Marshall in the MacIntyre Range, has since been named in honor of the brothers, and the brook which is the most popular approach has been named after their guide.
There are a substantial number of 46ers today, and those who climb all the peaks and file trip reports with the club historian are permitted to join the 46ers and receive a patch to commemorate the accomplishment. Members are also assigned a number in the order in which they joined. As of 2007 there are 6,212 who have met these requirements.
When aspirants have conquered their 30th peak, they start receiving the club newsletter. At the 40th, they are sent formal membership questionnaires.
The club also works to preserve the High Peaks and other areas of the Adirondacks, organizing regular trail maintenance trips.
Although the tradition is to climb the original 46 peaks, more recent surveys have shown that four of these peaks are actually lower than in elevation and another, MacNaughton Mountain, is actually just at despite earlier surveys that showed it at a lower elevation. All peaks have at least one maintained trail or thoroughly broken-in unmaintained trail.
Until 2000, the peaks with unmaintained trails had small canisters with a notebook inside for aspiring members to sign in. It was also at one time a requirement that aspirants visiting such peaks include, in their reports, the last three signatories.
Some go further and reclimb all the peaks in winter, and they are entitled upon completion of this to use a "W" after their membership numbers. This is a very difficult task due to the severity of winters in the Adirondacks. Some peaks, such as Gothics, can require some technical climbing skill when covered with snow and ice.
As of October 2007 there were 369 winter 46ers, or 6 % of the total all-time membership.