The definition of urban typomorphologies is fundamental both for the description as well as for the prescription of urban form. However, urban typomorphologies are traditionally defined through time-consuming analytical procedures, which are based mainly on the personal knowledge and ability of the analyst and on ad-hoc generalizations. Such generalizations are also usually context dependent and apparently not fit to deal with contemporary metropolitan and suburban forms, whose emergent and very different morphologies have until now eluded stringent classifications. In this paper we explore the possibility of defining urban typomorphologies through the use of nonsupervised hierarchical and non-hierarchical classification techniques, focusing on urban street patterns.