本文以大法官歷來相關解釋為素材，並佐以外國法相關見解的分析、比較，探討法律明確性原則之審查，首先指出明確性原則有預先告知與防止恣意執法功能，而大法官釋憲實務通行的可預見標準是根據預先告知功能發展而來，本文特別強調可否預見的審查原則上應採一般人可預見標準，不宜採法律人可預見標準，以避免法律明確性原則被形骸化。本文另根據釋字第445號解釋，分析大法官還曾採用與防止恣意執法功能相呼應的所謂選擇性執法標準，可惜此一標準在釋憲實務並未受到應有的重視。從釋字第276號解釋以來，本文發現大法官開展另一個規範密度面向的法律明確性審查，要求在法律要件或法律效果的規範方面，基本權侵害越嚴重者，重要事項越須以法律詳盡、完整規定。

This article analyzes how the Justices apply the Principle of Legal Certainty to check the constitutionality of the statutes challenged. It first explains the two rationales of the Principle of Legal Certainty, namely the prior notice and avoiding arbitrary enforcement. It explores then that the Justices apply not only the ”foreseeability” standard, which follows the first rationale and is most frequently used by the Justices, but also the so-called ”selective enforcement” standard, which follows the second rationale, but regretfully has been only once applied and deserves more attention. This article also takes notice that, according to the Justices, it exists another dimension of legal certainty, which concerns mainly the question, whether certain issues relevant to the fulfillment of human rights have been in detail and thoroughly provided by the statutes challenged.