Advance directive refers to a description of the treatment method a patient wants to be provided with in case where the person is unconscious or lacks an ability to decision making in a future period or a declaration of intention that delegates and appoints another person who makes a decision regarding a treatment method on behalf of the person. Advance directive is usually a document form, but oral statement is acceptable as well. Advance directive may have a variety of forms though, it basically consists of two basic forms. That is, one is a living will, and the other is a surrogate decision making. Though the importance of advance directive has been emphasized, and the necessity of adopting the system has been strongly argued for so far, the debates on criteria, method, and procedure alike have not yet reached an agreement. It is because even the concept of advance directive is more or less ambiguous, and each specific method has its own theoretical limitations and practical constraints. Thus the inquiries on advance directive raised in the study are summarized as the meaning, practicability, and philosophical foundation of the advance directive. Firstly, the theoretical limitations of Advance directive may be categorized into conceptual and moral limitations. In case of conceptual limitations, authors of advance directives may not be well aware, in advance, of the particular situation in which he or her will experience in the future, and patients may experience the change in his or her values and lack the understanding and information about the future situation due to the changes in treatment methods. In case of moral limitations, a patient has a limited moral autonomy right and self identity that have an impact on his or her preference. Secondly, in case of practical constraints for advance directive, there exist cultural features, low ratio of documentation, as patients themselves admit, and low predictability and stability of patient's own preference regarding life-sustaining care. And the problem of validity and accuracy in proxy's decision making is also raised. Those who administer a living will, especially, may have a difficulty in understanding the directive by a patient, so that the accuracy of execution cannot be secured. In the sense, it is needed to implement a legal device in order to solve such problems. In summary, it is urgently required to understand the limitations and explore desired alternatives to overcome the relevant problems in advance, which must contribute to successfully adopting and effectively operating the advance directive system in Korea.