Classification of vasculitis remains unsatisfactory. This is largely because the pathogenetic mechanisms of this family of related disorders have not been fully understood. Existing classification criteria are useful but limited. This has become more apparent with the advent of more effective and more specific therapies. A rational basis for classification could significantly improve our approach to treatment. The development of diagnostic criteria in vasculitis is an even greater challenge but may ultimately provide more useful for the non-specialist clinician. International efforts are underway to provide more effective classification and diagnostic criteria.