The Ramsar Convention text requires the Contracting Parties to respond to actual or potential changes in the 'ecological character' of their Ramsar Sites. After some years, the Convention's obligations relating to the conservation of these sites and to the 'wise use' of wetlands in general came to be defined in terms of 'maintaining' this character. Defining and operationalising these concepts has been complex. This paper reviews the evolution of this, and the challenges that remain in relation to issues such as choosing an appropriate baseline condition to describe, the kinds of changes that warrant a response and situations of natural fluctuation or 'regime shift', where 'maintaining' ecological character may be an unduly static aim. The 'character' of wetlands nevertheless remains a valuably integrative concept, preserving something of the holistic vision developed 50 years ago by the Convention's founders.