This thesis seeks to identify the psychosocial factors that influence adolescent smoking and to make suggestions for a smoking prevention/intervention programme. It is of particular interest to explore adolescent smoking in the Greek setting, where both teachers and pupils smoke on the school premises and smoking is socially acceptable. The participants are 672 pupils who attend six Greek schools - 351 aged 12-13 years old (mean age=12.6 years) and 321 aged 15-16 years old (mean age=15.8 years). Self-report, anonymous and confidential questionnaires are completed at the beginning and at the end of the academic year (7 months apart). The participants are grouped into four categories according to their smoking behaviour and 150 of them are randomly selected and interviewed. The interviews are semi-structured and employed to validate the self-reports and to provide more in-depth information on certain issues. Information on the situation in Greek schools is collected from 120 teachers who are interviewed at the beginning of the academic year. There is a significant increase in the smoking prevalence of both age groups at phase two. The patterns of the changes in smoking support the theory of stages. Psychosocial factors, such as school, teachers, parents, siblings and friends exert different levels of influence on the adolescents, who are not merely passive recipients. Personality factors are equally important determinants of the adolescents' decision to experiment with cigarettes and take up the habit of smoking or not. Adolescents foster many misconceptions about cigarettes, which may differ according to their gender. Their knowledge tends to mirror a reproduction of statements they do not fully understand. Intention to smoke in the future seems to be a fairly accurate predictor of taking up smoking eventually. Suggestions for smoking prevention/intervention programmes and a model of layers of influence on adolescent smoking are discussed.