Modern refineries have to respond to stiffer competition, lower margins, and increasingly stringent product and environmental specifications. The application of information technology (IT) via computer-aided process operation systems has been a key to the survival of refineries in the present competitive age of globalized economy. This chapter purports to examine the increasing roles of computers in refineries and the resulting impacts on operation, safety, quality control, and overall profitability as discussed with respect to the related concepts, benefits, challenges, and present status of applications. The chapter concludes by shedding light on the remaining issues to be addressed in the increasing implementation of computerized systems in refineries, including the resulting human impact brought especially to the role of a person operator.