Obesity is defined as an accumulation of excessive amounts of adipose tissue in the body; the disease predisposes to a variety of diseases including diabetes mellitus, osteoarthritis, and cardiorespiratory diseases.  In most animals, obesity is the result of an imbalance between energy intake and energy expenditure.  However, in reality, the underlying pathogenesis is far more complicated, involving a complex interaction of many genetic, behavioural, environmental and biological factors.  As such obesity is now considered to be a complex, multifactorial disease.  This lecture will discuss current thoughts on management of obesity in dogs and cats.