Interest differentiation and elevation are supposed to provide important information about a person's state of interest development, yet little is known about their development and criterion validity. The present study explored these constructs among a group of Swiss adolescents. Study 1 applied a cross-sectional design with 210 students in 11th grade. Study 2 applied a 1-year longitudinal design with 289 students in 7th to 8th grade. Gender, personality traits, and career exploration were significant predictors of state and development of differentiation and elevation. Increase in differentiation predicted increase in career decidedness above traits. Elevation could not predict increase in exploration behavior over traits. The results provide support for differentiation and elevation as important aspects of adolescents' vocational interests. (Contains 2 tables.)