One of the most perplexing topics in Mesoamerican ethnology is the customary(2) social unit that mediates relations between household (or domestic group) and community in Mesoamerican Indian and rural society (Nutini 1976:14; Thomas 1979:45; for the label rural, see Chambers and Young 1979). (Mesoamerica here refers to the most intensively studied portions of this region, central and southern Mexico and Guatemala, but the region also includes Belize, El Salvador, and small sections of Honduras, Nicaragua, and Costa Rica [Kirchhoff 1968:23; Weaver 1993:2].) Scholars routinely mention this social unit among the distinctive features of the region's social organization (e.g., Kirchhoff 1968:30; Redfield and Tax 1968:33; Wolf 1959:220). It is a prominent element in local identity, politics, and ceremonial life in many Indian and rural communities (Guiteras Holmes 1968:104; Thomas 1988:195). There is no consensus on its defining characteristics, however, or its prevalence (now and in the past), or its chief variants, or, very importantly, what it should be called for comparative purposes. These issues form the substance of this article, but I will propose a definition and an analytical label at this point to facilitate discussion. The social arrangement in question is simultaneously an institutionalized alliance of households (or domestic groups) and a formal community subdivision in a hierarchically ordered, vertically integrated, customary system of social organization. It is a social segment in the strict sense employed by Service (1962:18-19) and Firth (1964:60-62), one of a set of like units that relate to one another in an orderly fashion, and whose functions serve to integrate one level of social organization with another. The unit is identified often in the literature as the Mesoamerican barrio. For reasons explained further on, barrio is an unfortunate choice of label. The alternative I propose is customary subdivision. Not every unit of organization found at the level between household and community is a customary subdivision. Excluded are units whose only purpose is to serve civil-administrative needs, such as the noncustomary subdivisions known as municipal tenencias and town secciones or demarcaciones. These are externally imposed inventions for the purposes of tax collection, censuses, and so forth. They bear little or no relevance to community organization unless their boundaries happen to correspond with the community's customary subdivisions (Guiteras Holmes 1968:105; Hunt and Nash 1967:253ff.; Redfield 1928:287; Slade 1992:50). Likewise disqualified are customary social units devoted solely to the needs of their membership, such as informal surname groups and kindreds (Taggart 1976), ritual kinship bonds or compadrazgo (Nutini 1984; Nutini and Bell 1980), reciprocal exchange networks such as ayuda, vuelta mano, and guelaguetza (Nutini 1968; Stephen 1991), patron-client dyads (Foster 1961, 1963), political factions (Friedrich 1977; Hunt 1976), and voluntary religious fellowships (Dow 1974; Nash 1958:62-64). Customary subdivision systems, by contrast, exhibit these features: an established set of co-equal subdivisions; community rules for changing the number of recognized subdivisions; community rules for assigning subdivision affiliation, such that all or virtually all the households in the community are incorporated into the system; and the formal or informal authority to draft labor from the members for both the benefit of the constituent households and the benefit of the community (Kirchhoff in Guiteras Holmes 1968:117; Lockhart 1992:16; Mulhare 1986:396, 406-08). Many qualitatively different kinds of social arrangements serve as the basis for customary subdivision systems in Mesoamerica; e.g., descent groups, territorial wards, and less easily defined groups that merge kinship, territoriality, and other criteria in varying degrees. Several obstacles stand in the way of the systematic, comparative study of these systems: 1. …