Just in Time [JIT] means synchronising supply with demand so that supply arrives promptly just when the materials are needed. Traditionally, the way in which supply and demand were synchronised was to hold stock, but contemporary perspectives regard stock as muda, or waste. JIT is appropriate when demand can be forecast with accuracy and lead times are relatively predictable. Reducing inventory levels typically exposes supply chain problems such as part deliveries; poor quality materials and poor forecasts, so the systematic resolution of these problems can improve overall supply chain efficiency. See also Agility, Lean Thinking and Muda.