Public interest lawyers often bring large-scale cases against government defendants for injunctive relief as class actions. Until recently, their class certification motions routinely succeeded, enabling plaintiffs to obtain sweeping remedies that have required fundamental reforms to government policies and practices. In recent years, however, the law regulating the public interest class action has changed dramatically, with recurring doctrinal problems splitting the federal courts. Should a nascent trend against class certification continue, class action doctrine will soon present a formidable obstacle – possibly a barrier – to the successful prosecution of a sort of litigation that has produced innumerable changes to prisons, foster care systems, and other government agencies and services over the last fifty years. Any path out of the present confusion must address a basic but neglected question. Why do large-scale public interest cases so regularly proceed as class actions? The answer involves an under-appreciated interaction between the law of class actions and other doctrines devised to limit standing and the scope of remedies. Class action procedure enables public interest plaintiffs to vindicate policies in the substantive law consistent with broad, systemic remedies without asking courts to usurp power from other branches or adjudicate ineptly Without class certification, these policies would lie dormant, as the other doctrines would unnecessarily derail litigation. This “counterweight” function can generate responses to the doctrinal problems that courts have struggled to answer in this new era for the public interest class action. If class action procedure evolves in a manner consistent with its function, large-scale public interest litigation will remain a viable means for the achievement of structural reform.