Agreement is approached from the analytical decisions required for constructing a typological database. The Surrey Database of Agreement provides detailed, highly structured information on the agreement systems of fifteen genetically diverse languages. The range of material included and the criteria for inclusion are set out here. There is then detailed discussion of the difficult cases, in particular the dividing line between agreement markers and pronominal affixes. The criteria relevant to this distinction are in part drawn from the literature and in part new. The aim is that the criteria adopted should be fully clear, so that linguists of different persuasions can use the database for their varying purposes.