This paper discusses the research findings in voice mutation, vocal instruction, and the application of knowledge to vocal instruction. Much research involves changes in the male and female adolescent voices, especially of interest to choral directors and music educators. The research defines the vocal development categories as: (1) posture; (2) breath management; (3) relaxation; (4) phonation; (5) resonance; (6) registration; and (7) articulation. A segment on therapy and exercise suggests ways to develop the voice that has been abused. An extensive list of references offers further topics for research. (EH)