MDDBs (MultiDimensional Databases) are 'in' and SAS Institute is now offering MDDB software as a new product line. What exactly is an MDDB? Is there a simple explanation? The structure of an MDDS is not as complex as it might seem at first glance. This paper will discuss the structure of MDDBs as well as their uses. Access options and functionality will be covered. In addition, a short, personal overview of the pros and cons of this storage technique will be offered.