Work in process (WIP) or in-process inventory includes the set at large of unfinished items for products in a production process. These items are not yet completed but either just being fabricated or waiting in a queue for further processing or in a buffer storage. The term is used in production and supply chain management.

Work in progress is a key element in lean manufacturing. It is the single most important visual indicator reflecting the level of waste a system contain. And as we identified with this post inventory and WIP can be a waste by itself.

Optimal production management aims to minimize work in process. Work in process requires storage space, represents bound capital not disponible for investment and carries an inherent risk of earlier expiration of shelf life of the products. A queue leading to a production step shows that the step is well buffered for shortage in supplies from preceding steps, but may also indicate insufficient capacity to process the output from these preceding steps.