This chapter provides two narratives: a survey of the key units of work relationships, from small to large, and a discussion of work’s analytic characteristics, including causes of variation in these characteristics. The configuration of any contract at any point in time, however, is not a determinate outcome of short-run demands for quality, power, and efficiency but rather depends on a historically contingent bargaining process set within a cultural framework. Work contracts are organized cumulations of transactions; their non-work equivalents are social ties, which likewise always have some element of contract, however informal. Work contracts compound into networks, of which the most prominent work-based versions are markets and hierarchies. Organized, durable transactions cluster into implicit or explicit work contracts stipulating parties, rights, obligations, and sanctions to the transactions in question. Work contracts differ from mere accumulations of work transactions in featuring enforceable agreements that govern durations, limits, enforcement mechanisms, and relations among transactions.