The traditional approach to the diagnosis and management of chronic obstructive pulmonary disease (COPD), cardiovascular disease, and lung cancer has been to address each separately. Guidelines have documented the scientific basis for diagnosis and management, but have done little to explore the interconnections between them or to address comorbidity. The past few years have seen greater attention to the problem of chronic diseases and increased awareness of the impending crisis in health care as a result of the changing demographics of the world's population with a steady increase in life expectancy and a higher proportion living into the chronic disease age range. COPD presents a particular problem, as its mortality rate continues to climb steadily in most countries, particularly in women. The same is true for lung cancer. Cardiovascular disease mortality shows a different pattern, with deaths continuing to increase in developing countries but stabilizing or decreasing in resource-rich countries as aggressive strategies to diagnose and treat cardiovascular disease have been put into place. Predictions for 2020 from the Global Burden of Disease Study are that ischemic heart disease will stay the number one cause of death worldwide, COPD will go from sixth to third place, and lung cancer will go from tenth to fifth place. The purpose of this introduction is to set the stage for a review and discussion of the major comorbidities of COPD, heart disease, and lung cancer, to expand our understanding of the interrelationships among the "Big Three" diseases, causes of morbidity and mortality worldwide.