The global increase in the prevalence and incidence of obesity has called serious attention to this issue as a major public health concern. Obesity is associated with many chronic diseases, including cardiovascular disease and diabetes, and recently the role of overweight and obesity in lung disease has received new interest. Independently of obesity, diet also plays a role as a risk factor for many chronic diseases, and evidence is accumulating to support a role for diet in the prevention and management of several lung diseases. Chronic obstructive lung disease is the third-leading cause of death globally, and both obesity and diet appear to play roles in its pathophysiology. Obesity has been associated with decreased lung-function measures in population-based studies, with increased prevalence of several lung diseases and with compromised pulmonary function. In contrast, obesity has a protective effect against mortality in severe chronic obstructive pulmonary disease (COPD). Nutrient intake and dietary patterns have also been associated with lung-function measures and the development and progression of COPD. Taken together, this suggests that a focus on obesity and diet should be part of public health campaigns to reduce the burden of lung disease, and could have important implications for clinicians in the management of their patients. Future research should also focus on elucidating these relationships in diverse populations and age-groups, and on understanding the complex interaction between behavior, environment, and genetics in the development and progression of COPD. The goal of this article is to review current evidence regarding the role that obesity and diet play in the development of COPD, and in COPD-related outcomes.