Adolescence is an important time for emotional development. Recently, daily diary methods are increasingly employed in research on emotional development and are used to explore the development of and sex differences in emotions during adolescence. However, before drawing conclusions about sex differences and developmental trends, one needs to ensure that the same construct is measured across sex and time. The present study tested measurement invariance of daily emotion assessments across sex, short-term (days within weeks) and long-term periods (days across years) in a sample of 394 adolescents (55.6% male) that were followed from ages 13 to 18. Moreover, the study examined the developmental trajectories of adolescent emotional experiences. Adolescents rated their daily emotions (happiness, anger, sadness, anxiety) during each day of a normal school week (Monday to Friday) for 3 weeks per year for 5 years (i.e., 15 weeks × 5 days = 75 assessments in total). Measurement invariance analyses suggest that the measurement of adolescent daily mood was invariant between boys and girls and across shorter and longer time intervals. Moreover, latent growth curve analyses showed that happiness decreased from early to middle adolescence, whereas anger, sadness, and anxiety increased. Anger returned to baseline toward late adolescence. In contrast, the decrease of happiness and the increase of anxiety leveled off without reversing, whereas sadness continued to increase. The discussion highlights the implications of measurement invariance in research on individual and developmental differences and discusses the findings in light of normative emotional development.