This chapter examines the evolution and eventual decline of the Lemon test, which served as the dominant framework for Establishment Clause jurisprudence for over five decades. Originating from the 1971 Supreme Court decision in Lemon v. Kurtzman, the tripartite test required government actions to have a secular purpose, neither advance nor inhibit religion as their primary effect, and avoid excessive entanglement between government and religion. The chapter traces the test’s application across various contexts, from government funding of parochial schools to religious expression in public educational settings. The analysis reveals how the Lemon test faced immediate and sustained criticism from across the ideological spectrum, with the Court subsequently developing alternative frameworks including the endorsement test and coercion test. Through examination of key cases spanning the 1970s through 2020s, the chapter demonstrates how conservative justices, particularly Justice Antonin Scalia, mounted sustained attacks on Lemon’s validity and consistency. The chapter documents how the test’s application became increasingly inconsistent, with the Court selectively invoking or abandoning it depending on the desired outcomes. The chapter concludes by analyzing the test’s effective demise in recent decisions, particularly American Legion v. American Humanist Association (2019) and Kennedy v. Bremerton School District (2022), where multiple justices declared Lemon “dead” or called it a “misadventure.” While the Court has not formally overturned Lemon, the chapter argues that its practical authority has been thoroughly undermined, leaving Establishment Clause jurisprudence in a state of doctrinal uncertainty as the Court moves toward a more accommodating approach to church-state relations. This transformation represents a fundamental shift in constitutional interpretation with significant implications for religious liberty and separation of church and state in American public life.