For decades, professionals in applied mathematics and mathematical puzzle fans from all over the world supplied provocative problems to the puzzle columns of the Upon the appearance of an interesting problem, readers wrote in to the suggesting new approaches to the solution, some greatly simplifying the problem and others broadening its scope. This collection presents 52 of the finest problems, all featuring the "surprise attack" and abounding in imaginative and interesting solutions. The problems involve measurement of geometrical spaces, probabilities, distances, number systems other than the decimal, interesting number relations, relative motion, and the discovery of the simplest solution through purely logical means. Solutions involve such techniques as arithmetic, algebra and geometry, number theory, statistics, networks, and inversion. Several approaches to the solution accompany each problem, and even the best of these represent not the ideal solution but only the most satisfying — so far.