On behalf of the Mood Disorders Society of Canada (MDSC), I am pleased to present the fourth edition of “Quick Facts on Mental Illness & Addiction in Canada”. In keeping up with the many changes that have occurred within the mental health field within the past ten years, we felt it was important that this resource be updated to reflect these changes. The incredible demand for copies of the first three editions has been phenomenal. There is now no doubt that there is a need in Canada to bring together, a comprehensive, evidence-based document containing important statistics relating to mental illnesses and addictions. The impact on individuals and their families, the healthcare system, the workplace, and the economy, in general, is extremely significant. There is also a need to develop a common understanding of the relationship between mental illnesses, addictions, and physical illnesses such as cancer, diabetes, and heart disease. We are certain that you will find this fourth edition useful and very informative.