Introduction to the Special Issue Honoring Bob and Ellen Kaplan

In 1994, Bob and Ellen Kaplan embarked together with other friends and colleagues on a wonderful adventure. Friends had lamented that there was a lack of high-quality math learning experiences for kids along the lines of the Math Circles offered in the former Soviet Union, so the Kaplans decided to do something about it. This special issue is dedicated to a remembrance of that adventure and its impact on the mathematical and personal development of many people.