The paper examines the ramifications of naturalism with regard to the question of individuality in economics and biology. Economic theory has to deal with whether households, firms, and states are individuals or are mere entities such as clubs, networks, and coalitions. Biological theory has to deal with the same question with regard to cells, organisms, family packs, and colonies. To wit, the question of individuality in both disciplines involves three separate problems: the metaphysical, phenomenist, and ontological. The metaphysical (...) class='Hi'>problem is concerned with purposeful action: Is the firm or organism exclusively the product of efficient causality (optimization) or is it motivated by final causality (purposefulness)? The phenomenist problem is interested in the substantiality of essences: Is the firm''s or organism''s scheme of institutions/traits deep or is it extraneous to identity? The ontological problem is related to the issue of reductionism: Is the behavior of lower-level organization governed by a pre-constituted entities or is it context-sensitive? The paper finds that theoretical differences run along the naturalist/anti-naturalist divide rather than along disciplinary specialization. Also, the paper finds that it is not inconsistent for the same theorist to be naturalist with regard to one problem and anti-naturalist with respect to the other two problems. (shrink)