A major concern in the operation of cooling tower systems is the prevention of scale on heat transfer and evaporative surfaces. The process by which scale forms is not often clear or well explained@ and the means by which scaling may be controlled is commonly not explained to any significant degree. This paper attempts to outline the mechanisms of scale formation@ discuss chemically and non-chemically based strategies for scale control@ provide real-time instrumental data illustrating the effectiveness of both chemical and non-chemical control and then discuss the basic requirements for successful implementation of each strategy given the many chemical@ physical and operational variables generally associated with cooling tower operation. Each strategy has its advantages and disadvantages and no one strategy is well suited to all circumstances. It is hoped that this paper will help clear up some of the misconceptions concerning chemical and non-chemical cooling water treatment and promote more meaningful and informed discussion during the treatment strategy selection process.