Adolescence is the transition from childhood to adulthood; puberty is characterized by growth in stature and sexual maturation.
Puberty and adolescence do not necessarily go hand-in-hand. Many girls start puberty before the age of nine but continue to act their chronological age. In contrast, teens with delayed puberty due to hypogonadism (e.g., Turner Syndrome) or constitutional delay (e.g., late-bloomers) mostly act like adolescents.
Teen behavior is popularly attributed to "raging hormones," but sex steroid levels do not correlate with these behaviors, except that testosterone is associated with aggression. Over the last decade it has been found that typical "teenage behaviors" and increased cognitive abilities are due not to hormones but to growth and pruning of the neuronal processes in the brain.
The mean age of puberty has trended downward for decades. Onset of puberty for girls normally occurs between the ages of 8 and 13.4 years. In boys, onset is considered to be normal between 9 and 14.0 years.