On farm conservation of crop diversity poses obvious policy challenges in terms of the design of appropriate incentive mechanisms and possible trade-offs between conservation and productivity. This paper compares factors explaining the inter-specific diversity (diversity among species) and infra-specific diversity (diversity among varieties within a species) of cereal crops grown in communities and on individual farms in the northern Ethiopian highlands. Using named varieties and ecological indices of spatial diversity (richness, evenness, and inverse dominance), we find that a combination of factors related to the agro-ecology of a community, its access to markets, and the characteristics of its households and farms significantly affect both the inter- and infra-specific diversity of cereal crops. Factors that explain variation among communities in either the inter- or the infra-specific diversity of cereal crops differ markedly between Amhara and Tigray, underscoring the location-specific nature of any policies designed to support conservation. Policies appear neutral to the type of diversity maintained. That is, there are no apparent trade-offs between policies seeking to enhance the richness or the equitability among cereal crops or within any single crop grown in communities. Trade-offs may occur among crops, however. Policies that shape the access of communities and individual households to critical production assets such as land, labor, oxen and livestock will have significant implications for both the inter- and infra-specific diversity among the cereal crops they grow, differentially among crops. Education is usually positively related to both inter- and infra-specific diversity. As adult male labor is drawn out of farm production into non-farm activities, the diversity among cereal crops will decline, though households headed by women or with more adult women appear to have higher levels of infra-specific diversity. Growing modern varieties has no apparent effect on diversity of maize and wheat, supporting the conclusion that in the northern Ethiopian highlands there may be no trade-off between seeking to enhance productivity through the use of modern varieties and the spatial diversity among named varieties of these cereal crops. So far, introduction of modern varieties has not meant that any single variety dominates or that modern varieties have displaced landraces, most likely because they have limited adaptation and farmers face many economic constraints in this environment. Landlessness and farm physical factors have differential impacts at the community and household levels. The role of markets in introducing or reducing cereal crop diversity is revealed to be ambiguous when we examine different geographical scales of analysis and inter- vs. infra-specific dimensions. If agrobiodiversity conservation is to be seriously considered as a policy option in these communities, applied economics researchers will need to 1) establish the relationship of cereal diversity conservation to private and social welfare, and 2) articulate the relationship between the names of varieties managed by farmers and infra-specific, genetic diversity measured through agro-morphological or molecular analysis. Methodological advance may be required to relate policies to diversity outcomes measured at various geographical scales or levels of aggregation in the same farming system. Specific issues for further social science research include the relationship of seed management practices, seed markets, tenure and soil conservation practices to diversity conservation, and the possible application of bio-economic models to the analysis of species and genetic diversity interactions with farming systems. For policy purposes, it will be important to better understand the particular institutional and social elements that cause communities to behave differently in terms of conservation than the individual household farms of which they are composed, and for some communities to conserve more than others.