The CellML language is an XML-based specification for representing mathematical models of biological processes. The University of Auckland's Bioengineering Institute is committed to creating tools and evolving the language so that biologists and modelers can build, understand, and share models. The CellML standard and tool developments are open source; we encourage researchers and software developers to become involved in the process. The model repository already has a large array of biological models; we expect this to grow rapidly as more researchers adopt the tools and modelling environments we offer which encourages the reuse and sharing of models.