Cam is the latest in a series of global atmospheric models, formerly known as CCM (community climate model), developed for weather and climate research groups. Cam plays an increasingly important role in the study of atmospheric composition of CCSM (community climate system model). Cam requirements are broadly classified into scientific requirements and software requirements. Cam implements scientific algorithms according to scientific requirements. Changes in scientific requirements usually change the scope of model simulation. Software requirements involve the unscientific part of the model. More about the usability, maintainability and scalability of the model.