GLIMMER is a set of libraries, utilities and example climate drivers used to simulate ice sheet evolution. At its core, it implements the standard, shallow-ice representation of ice sheet dynamics. This approach to ice sheet modelling is well-established, as are the numerical methods used. What is innovative about GLIMMER is its design, which is motivated by the desire to create an ice modelling system which is easy to interface to a wide variety of climate models, without the user having to have a detailed knowledge of its inner workings. This is achieved by several means, including the provision of a well-defined code interface to the model, as well as the adoption of a very modular design. The model is coded almost entirely in standards-compliant Fortran 95, and extensive use is made of the advances features of that language.