The debate in Hong Kong over which language (Cantonese, Mandarin or English) should be used as the teaching medium in publicly funded educational institutions predates the city's transition from colony to Special Administrative Region in 1997. In the past nine years it has been presented as the cornerstone of the ongoing educational reform process. This paper argues that the issue has become increasingly ideologically motivated since the end of the colonial period, and identifies two factors contributing to the decision-making process in Hong Kong: the role of outside vested interests in educational policymaking and the shortfall in specific language teaching expertise. Against the complex background of Hong Kong's official language policy of "trilingualism and biliteracy", the paper shows how educational policymakers are constrained by these factors and prevented from engaging in substantive educational language planning as a starting point for root-and-branch reforms, and how this may have led them to commission research to support pre-existing executive decisions. The study analyses official statements and policy documents on the medium of instruction issue, in combination with observations of the current situation in publicly funded secondary schools, in an attempt to indicate future directions for Hong Kong.