In 1925-26, the late Max Born gave two sets of lectures at M.I.T., one on the structure of the atom, the other on the lattice theory of rigid bodies. Problems of Atomic Dynamics contains the text of both sets. What gives this volume its remarkable interest is just those dates: 1925-26. This must have been, by all accounts, the headiest period in twentieth-century physics, and Max Born was one of the leaders of the ferment. As Norbert Wiener remembers, "When Professor Born came to the United States [for these lectures in 1925] he was enormously excited about the new basis Heisenberg had just given for the quantum theory of the atom." These lectures represent perhaps the most vivid written record of the transition between the "old" quantum theory of Bohr, and the "new" theory. "At the time I began this course of lectures," Born writes, "Heisenberg's first paper on the new quantum theory had just appeared. Here his masterly treatment gave the quantum theory an entirely new turn. The paper of Jordan and myself, in which we recognized the matrix calculus as the proper formulation of Heisenberg's ideas, was in press, and the manuscript of a third paper by the three of us was almost completed." Even as the lecture series progressed, Born became familiar with new results, which he introduced into his presentation: Pauli's fourth quantum number, Dirac's formalism, his own work on a general operational calculus. And yet, in spite of the conditions of revolutionary changes in physics that year--in which established ancient regime principles were collapsing almost monthly--the theory is developed with a cool elegance and with a formal completeness which may be regarded as a "limiting case" of its current state. These lectures represent the foundations of quantum theory, and they have withstood the tests of time--the tests of more than forty years of experimental evidence.