HarperCollins has appointed Maureen O'Brien as executive editor at Morrow/Avon. O'Brien, who starts April 1, will acquire commercial fiction and nonfiction for the HarperEntertainment imprint as well as for the entire Morrow/Avon division. She will report to Morrow/Avon publisher and executive v-p Michael Morrison. O'Brien most recently served as an editor at Hyperion. Prior to joining Hyperion, O'Brien had been an editor with the New York Post and Publishers Weekly.