To respect an individual’s autonomy and dignity, Thai laws provide the right for a patient to make an advance decision concerning their medical treatment. With specific legal rules on advance directives, Thailand has a comprehensive approach to the regulation of advance directives. Since the law simply requires a patient to be competent while making an advance directive, with no strict format except that it must be done in writing, it seems easy to make an advance directive in Thailand. However, the loose format of advance directives might not ensure their effective application in practice. This chapter begins by exploring the regulations on advance directives, including the requirements for a lawful advance directive and its execution, followed by the scrutinising of practical problems regarding their application. The role of ethical values, as well as social and cultural influences, will then be discussed to explain the legal rules and practice of advance directives in Thailand. The chapter ends with suggestions regarding additional requirements for advance directives to address problems surrounding their application, as well as better guidelines for the healthcare professions, so that the aims of the laws on advance directives – to protect an individual’s autonomy and dignity – can be actually achieved.