In Hong Kong, compulsory admission is governed by the Mental Health Ordinance Section 31 (detention of a patient under observation), Section 32 (extension of period of detention for such a patient), Section 36 (detention of certified patients), and the sections in Part IV for hospital order, transfer order, and removal order. Mental health professionals adopt both legal criteria and practice criteria for compulsory admission. The present study discusses the harm principle, the patient's decision-making capacity, the multi-axial framework for compulsory admission, and the balance between paternalism and patient liberty.