William H. McClain is an American molecular biologist and academic. He is currently Halvorson Professor of Bacteriology and Molecular Biology, Emeritus, at the University of Wisconsin-Madison. McClain is a Fellow of the American Academy of Arts and Sciences, and, formerly, a Jane Coffin Childs Memorial Fund for Medical Research Fellow. He was a Board Member of the American Academy of Arts and Sciences, Midwest Center. McClain is a pioneer in the biological sciences known for the dissection of RNA-protein recognition primarily through genetic and biochemical means in bacteria.