This chapter focusing on US law first sets out the underlying rule against horizontal price-fixing—and many other forms of horizontal economic coordination beyond firm boundaries—that most directly implicates collective action among workers and other small players in the economy. It then briefly sets out the legal landscape of the various antitrust exemptions that can nevertheless shield such collective action from scrutiny: the labor exemption (exploring the relationship between the law in this area and the contemporary ‘fissured workplace’), the state action exemption, the various agricultural exemptions, and the lack of an exemption for small and medium-sized enterprises (despite sporadic movements toward such an exemption). While primarily descriptive, the chapter highlights the legal construction of economic coordination and competition from the ground-up—rather than preexisting ‘market competition’ regulated by law—and the largely invisible background role of firm-based coordination as the most significant antitrust exception of them all.