Mineral scale formation is a problem across many industries and in diverse applications and equipment. Each application may have specific characteristics that must be taken into account if a modelling system is to be reasonably accurate. The modelling of cooling water and oil field production chemistry have been studied extensively since the 1970’s and state-of-the-art physical chemistry models devloped to simulate them with acceptable accuracy even under extreme conditions.Open recirculating cooling water predictive models for example must incorporate algorithms to concentrate the water treating the process as an “open” system and address cooling stem specific situations including pH control methods and even the impact of chlorination. pH prediction of the concentrated recirculating water is a key requirement.Oil and gas production chemistry modelling presents another set of unique challenges including the distribution of gasses such carbon dioxide and hydrogen sulfide between phases as a brine transitions from bottom hole conditions to the well head and then flashes at the separator. Such a system must incorporate algorithms to treat the process as a “closed” system and partition the critical gasses between phases with pressure and temperature changes and account for the impact of the sometimes dramatic environmental parameter changes upon pH solubility and physical constants.Membrane systems did not begin to receive the same rigorous treatment as oil and gas production cooling water and applications such as geothermal power production until the 1990’s. Much of the software in use by the industry relies upon simple index calculations on the level of the Langelier Saturation Index and saturation indices based upon total analytical values. The mainstream reverse osmosis application specific software generally used is not up to the rigors of high ionic strength high recovery and water reuse membrane systems. They are definitely not capable of adequately modelling cascade systems. The simple indices used for predicting scale formation and as driving forces for dosage optimization do not simulate high ionic strength activity coefficients and near as well as far effects. The simple models fail to account for speciation and the ion association of even such standard (yet critical) pairs such as CaSO4o aqueous.Scale inhibitor models in these simple models also do not account for inhibitor dissociation and the active form of the molecules. They also tend to lack the sophistication of models used in other applications which necessitate an induction time extension approach. Without adequate speciation models inhibitor solubility can not be adequately taken into account or insoluble forms controlled predictably.They also ignore in many cases application specific challenges such as membrane specific ion rejection pH prediction and control in vented (open) or tight (closed) systems and concentration polarization at the membrane water interfaceThis paper discusses the practical application of advanced physical chemistry techniques commonly employed in cooling water and oil field chemistry to application specific modelling of mineral scale formation and control in membrane systems.The techniques are discussed and applied to:· Predicting scale formation;· Identifying the upper driving force limit for inhibitors and blends;· Developing inhibitor models for minimum effective dosage; and· Developing models for preventing failure due to inhibitor solubility.The methods discussed have been validated in field applications.