Research on the relationships between sex and gender and respiratory health suggests an impact on incidence, susceptibility and life-course pattern for respiratory diseases. This chapter reviews evidence of the impact of sex and gender on smoking, lung cancer, COPD and asthma, and outlines the possible mechanisms underlying gender differences.Worldwide, reductions in age-standardised daily smoking rates have been reported since 1980 from 41.2% to 31.1% for men, and from 10.6% to 6.2% for women. Gender differences in smoking affect the rates of lung cancer and COPD, which are on the increase worldwide, varying considerably across regions and countries. Sex ratios of asthma rates are more homogenous (around 1.2 to 1.5), but exhibit a characteristic lifetime pattern.Considerable gender differences are reported for smoking, lung cancer, COPD and asthma. To improve the quality and effectiveness of healthcare by gender sensitive approaches, we need unbiased comparisons of men and women and insights into the mechanisms involved in producing sex and gender differences.