  The Atacama Large Aperture Submillimeter Telescope (AtLAST) is a concept for
a 50m class single-dish telescope that will provide high sensitivity, fast
mapping of the (sub-)millimeter sky. Expected to be powered by renewable energy
sources, and to be constructed in the Atacama desert in the 2030s, AtLAST's
suite of up to six state-of-the-art instruments will take advantage of its
large field of view and high throughput to deliver efficient continuum and
spectroscopic observations of the faint, large-scale emission that eludes
current facilities. Here we present the key science drivers for the telescope
characteristics, and discuss constraints that the transformational science
goals place on future instrumentation.
