The tremendous amount of published research, performed in the past two decades, has contributed to advances in RO desalination technology, although it is considered that key issues have been addressed inefficiently and unsatisfactorily. In this lecture, R&D priorities will be outlined and weaknesses of presently used approaches to address these issues will be indicated. To facilitate progress, a generalized methodology will be presented, relying on two main pillars; i.e.

• R&D work at small scale, dealing mainly with a) membrane material development, b) membrane module design and spacers, c) operating issues (fouling, scaling, monitoring).

• A comprehensive framework for RO process modeling/simulation at large scale, utilizing results from the above small-scale studies, that will cater to the needs of designing and operating desalination plants.

  The challenges and approaches will be reviewed in integrating information from studies at small-scale into a large-scale model. Emphasis will be placed on systematizing (or setting targets of) small-scale/laboratory work to serve multiple objectives; i.e. in addition to gaining improved understanding of particular phenomena, to obtain correlations of key parameters (representative of these phenomena) to be directly used in practice as well as provide the necessary input for model/simulator development. Progress made so far and prospects in implementing this methodology will be summarized.