Osmotic drug delivery system (ODDS) utilizes the basic principle of osmotic pressure for controlled release of drugs. It provides the release of drugs in controlled manner to maintain drug concentration within therapeutic window and minimizing toxic effects. ODDS delivers a drug to large extent is independent of the physiological factors of the gastrointestinal tract, pH etc. That is why it can be utilized for systemic as well as targeted delivery of drugs. The drug release from osmotic system controls the drug release by controlling various formulation factors such as solubility, osmotic pressure of the core components, size of the delivery orifice and nature of the rate controlling membrane. The design of osmotic system is achieved by optimizing formulation and processing factors to deliver drugs in preprogrammed rate and controlled manner. The present study explains about an update on osmosis, different types of osmotic systems, components of ODDS, key parameter sand some patents.