Over the past few years, there has been increased interest in large diameter reverse osmosis (RO) elements. The largest commercially available element format has an 18-inch diameter. There is now over 25 MGD of production capacity of RO systems using this element platform, and more systems are currently in the engineering phase. This paper describes operating plants where large diameter reverse osmosis (RO) elements were used, including the reasons why large diameter elements were selected for specific projects. The plants to be discussed cover both municipal and industrial water reuse and potable water production, and operation with a wide-range of membrane types and different pretreatment schemes. The plants include: the City of Waupun, Wisconsin; Tate-Monroe Water Association, Ohio; Joe White Maltings, Australia; and, Bundamba Advanced Water Treatment Plant, Queensland, Australia. Includes 6 references, tables, figures.