This is an electronic edition of the 1980 lecture notes distributed by Princeton University. The text was typed in TeX by Sheila Newbery, who also scanned the figures. Typos have been corrected (and probably others introduced), but otherwise no attempt has been made to update the contents. Genevieve Walsh compiled the index. Numbers on the right margin correspond to the original edition's page numbers. Thurston's Three-Dimensional Geometry and Topology, Volume 1 (Princeton University Press, 1997) is a considerable expansion of the first few chapters of these notes. Later chapters have not yet appeared in book form.