Fiedler’s contingency theory has been instrumental in understanding leadership effectiveness as a function of matching leadership style and situational demands. This article examines the theory’s historical evolution, core components, and empirical applications from 1980 to 2022. Findings indicate that Fiedler’s model—first introduced in 1967—established leadership style as a relatively stable, experience-based attribute, assessed primarily through the Least Preferred Coworker (LPC) Scale. Over the past 30 years, the theory has been applied across multiple disciplines, including nursing, education, industrial psychology, and international management. Studies during the 1980s and 1990s focused on leadership style assessment and the LPC’s psychometric refinement, while later research expanded its use across cultural contexts, such as Iran, Portugal, and Estonia. This chapter concludes that Fiedler’s model reliably aids organizations in diagnosing and optimally placing leaders, validating its status as a foundational tool in organizational leadership assessment.