The study of ultracold atoms and molecules is now the frontier of low-temperature science, reaching temperatures of a few hundred picokelvin above absolute zero. This field was made possible by a technique that did not exist 30 years ago: laser cooling of atoms. It is hardly obvious that the laser, which produces the most intense light on Earth and is routinely used in industrial applications for cutting and welding medal, would also provide the most powerful coolant. Such are the surprises of science, where a breakthrough in one area transforms others in unexpected ways. Since 1997, eight Nobel Laureates in physics have been recognized for contributions to ultracold atomic and molecular science, which has become one of the most vibrant fields in physics, cutting across traditional disciplinary boundaries, e.g., atomic, molecular, and optical; condensed matter; statistical physics; and nuclear and particle physics. This field builds on two accomplishments that it was the first to achieve: first, the production of quantum degenerate matter using a wide range of elements and, second, exquisite control of quantum degenerate matter at the atomic level. These have led to record low temperatures, ultraprecise atomic clocks, and new forms of quantum matter that generalize ideas from magnetism superconductivity and graphene physics.