The article examines the historical rise and institutionalization of the agency shop in public sector labor relations and its sudden fall in the Supreme Court’s Janus v. AFSCME, Council 31 decision.  The authors demonstrate that the rapid rise of public sector unionism took place during a period when most state laws did not require or even permit the agency shop.  We also explore the history of the agency shop in New York including the leading role New York City government played in advocating in Albany for legal changes to permit the agency shop to be negotiated.  The article then describe the swift fall from grace of the agency shop resulting from a series of United States Supreme Court 5-4 decisions culminating in the 2018 Janus decision.  Finally, the article discusses ways that state governments and state actors might act in response to the decision, along with the important public policy and legal ramification so the decision.