With the rise of globalization and the spread of English, English-medium instruction (EMI) has become a common practice among higher education institutions around the world. In the past two decades, many South Korean universities have also established and implemented institution-wide EMI policies. Using Ricento and Hornberger’s (1996) metaphor of the language planning and policy (LPP) onion as a heuristic, this paper looks at the different LPP layers involved in shaping these institutional EMI policies and describes how the global EMI phenomenon has been taken up in the South Korean national and institutional contexts. Furthermore, this paper elucidates the motivations, beliefs, and attitudes of different LPP actors and how they may overlap or conflict with one another across and within layers. Investigating the multilayered nature of EMI policies reveals how the unilateral and mandatory nature of initial planning, which failed to take into account the varying positions of stakeholders, led to many of the problems associated with EMI.