The Catskill Mountain 3500 Club, incorporated as the Catskill 3500 Club and often just referred to as the 3500 Club, is a peakbagging organization for hikers in the Catskill Mountains of New York. Those wishing to become members must climb all 35 Catskill High Peaks and, in a departure from the requirements of most other such clubs, climb Slide, Blackhead, Balsam and Panther mountains again in winter, which is defined by the Club's by-laws as the period from December 21 to March 21 regardless of the actual occurrences of the winter solstice and vernal equinox in particular years. The Club also awards a separate patch for those who go on to climb all 35 peaks during winter.