William "Bill" Yslas Vélez is an American mathematician, a current Emeritus Professor at the University of Arizona, and an Elected Fellow of the American Association for the Advancement of Science.

[1] From 1992–96, Vélez served as the president of Society for the Advancement of Chicanos/Hispanics and Native Americans in Science (SACNAS).

His doctoral thesis was written under the supervision of H. B. Mann.

Vélez became a Fellow of the American Mathematical Society in January 2013.

[3] In 2017, he was selected as a fellow of the Association for Women in Mathematics in the inaugural class.