Technological innovations and economic advances have led to increases in physical inactivity and sedentary behaviour (i.e., sitting). Evidence now indicates that it is not only necessary to be physically active at a moderate intensity for at least 150 minutes a week, but it is also important to limit the number of hours spent sitting. Over the past decade a wealth of epidemiological evidence has emerged suggesting that sedentary behaviour is associated with an increased risk of chronic disease (e.g., type 2 diabetes, cardiovascular disease, some cancers) and mortality. Acute experimental studies have shown that interrupting sitting with short (2-5mins) but frequent bouts of light intensity activity (standing, stepping and simple body weight exercises) throughout the day improves markers of cardiometabolic health. As such, interventions to reduce sitting time and break up prolonged sitting with light activity have been developed and evaluated, mainly in the workplace. This presentation will discuss this evidence, the strength of the evidence, how much sitting is too much, how much moderate activity is needed to eliminate the risk associated with high sitting time and how successful sitting reductions interventions have been.