Chronic diseases have a variable impact on men and women due to the complex interaction between biological sex and environmental risk factors to which men and women are differentially exposed. Sex differences have not been adequately explored in chronic obstructive pulmonary disease (COPD), as most studies have either had small sample sizes or not enough women to allow for accurate comparisons. This article will address sex differences in susceptibility, expression of COPD subtypes, and activity-related breathlessness, and will identify key areas for further investigation.