The collection of the concepts that are discussed in a document set can be represented by a geometric structure, called simplical complex, of combinatorial topology. A simplex is a high-frequency keywordset that co-occurs closely which, we believe, carries a concept in the document set. The collection of all these simplexes that forms the simplical complex represents the structure of these concepts. Based on the topological structure of this complex, the documents are clustered. Several clustering schemes are presented. Our initial experiments, as expected, do support the theory.