This article presents an overview of the automation systems for a semiconductor fab. In particular, two key systems are presented: 1) a manufacturing execution systems (MES) that formulates manufacturing methods and procedures and 2) a cell controller (C/C) that serves as the automation link between the upper MES and the lower equipment within a production tunnel. At the end of the article, lot operation of one manufacturing step is detailed to highlight the interaction between MES and C/C in a fully automated semiconductor fab. The C/C, in contrast, are to respond to equipment requests for processing, to coordinate intrabay or interbay lot transportation, and to keep the MES the most updated WIP information within a production channel. This overview presents the most essential automation functions needed in general semiconductor fabs. Yet, in terms of future technology trends, reported work on specification, design methods, and implementation platforms has taken advantage of the latest development of computer technology in general, and object-oriented technology in particular.