The handling and processing of powders can cause problems unless appropriate steps are taken when storing and transporting them - especially when made up of fine particles. The present chapter will consider the storage of powders in hoppers and their discharge. As far back as man has harvested and stored crops, people have stored particulate solids. Prior to 1960, the design of storage bins was an art. This changed when Andrew W. Jenike identified the criteria that affect material flow in storage bins. A proper hopper design is based on the flow properties of the bulk solid to be stored and a thorough understanding of these properties is mandatory.