SWiM is a semantic wiki for collaboratively building, editing and browsing a mathematical knowledge base. Its pages, containing mathematical theories or content dictionaries, are stored in OMDoc or OpenMath, both being markup format for mathematical knowledge. Our long-term objective is to develop a software that facilitates the creation of a shared, public collection of mathematical knowledge (e.g. for education) and serves work groups of mathematicians as a tool for collaborative development of new theories.