In Hong Kong, three principal languages co-exist: Cantonese, English and Putonghua. For more than two decades, among policy-makers and educators, there has been a substantial debate on the language policies governing the three principal languages. Since the political transition in 1997, the Hong Kong government has made a series of language policy reforms trying to create a reasonable balance among the three languages, and a “biliterate and trilingual” policy has been adopted, with the aim of enabling Hong Kong residents to become biliterate in written Chinese and English, and trilingual in Cantonese, Putonghua and spoken English. The policy is now guiding the curriculum design in Hong Kong language education. However, currently, Hong Kong primary schools do not have an agreed approach or method for the implementation of trilingual education, and there is an urgent need to explore current successful or unsuccessful models. After a comprehensive historical review of the development of language education in Hong Kong schools, this study aims to find out how the ‘biliterate' and ‘trilingual' language policy is currently implemented in Hong Kong primary schools. A large scale questionnaire survey were carried out among Hong Kong primary school principals on how trilingual education was implemented in the schools. The findings suggest that, from school to school, the implementation of trilingual education varied significantly, and the effectiveness of the trilingual education models varied as well. It is hoped that this study will help us to gain a better understanding of trilingual education in Hong Kong, and the study could lead to some insightful and theoretical contributions to multilingual education in general.