Phosphate based corrosion and scale inhibitor programs emerged as the cooling water technology of choice when the water treatment industry was strongly encouraged to eliminate chromates some 35 years ago. At the time we were certainly aware of the control without forming phosphate deposits on hot bundles problems with admiralty brass corrosion using only azoles, and troubles with well water iron and aluminum carryover interacting with the phosphate and escalating dispersant demand. Of course, we could see the increased algae growth on the towers, and covered many tower decks and increased chlorine and biocide usage in response. We were also aware of impending phosphorus-based cooling water programs because there simply persisted in perfecting phosphorus-based cooling water programs, because there simply was no reasonable alternative… until now. This paper describes the development of a promising phosphorus free corrosion and deposit control program including laboratory and field application performance data in several challenging applications.