This chapter summarises the principal results of Greenberg’s classic 1963 paper (Some universals of grammar with particular reference to the order of meaningful elements. In Joseph H. Greenberg (ed.), Universals of Language , 58–90. Cambridge, Mass.: MIT Press) and subsequent work in language typology developing Greenberg’s ideas by Lehmann, Vennemann, Hawkins and Dryer, concluding with a section on X’-theory and the Head Parameter.