China resumed its sovereignty over Hong Kong in 1997. Since then drastic changes in this former British colony have occurred. One of these changes is a shift in language policy, from bilingualism (Cantonese and English) to trilingualism (Cantonese, English and Putonghua). The present study is aimed at investigating tertiary students' use of Cantonese, English and Putonghua on a daily basis, analysing the roles and functions of each language and discussing how these may impact on language policy and language education. Research instruments included 52 students' language diaries and written analyses, 51 hours of audio-recordings of verbal exchanges, and focus group semi-structured interviews. Results show that the students' speech repertoire mainly consists of two languages: Cantonese and English and their various mixes. Cantonese is used to ensure understanding, consolidate solidarity and maintain social cohesion. The English-Cantonese mix has become a more powerful identity marker for educated people in Hong Kong than pure Cantonese. English and its supplement with Cantonese are often used in the domain of education. The majority of students seldom use Putonghua in everyday life, but there is a strong instrumental motivation to learn it. Measures are suggested to facilitate a more successful move from bilingualism to trilingualism. (Contains 1 table.)