The common good is a fundamental term which is included in both canon law and secular law. However, the way of perceive this concept under these two different legal systems differs fundamentally. In canon law, the common good is usually referred to the political and ecclesiastical community. The common good of the Church is connected with the realisation of the community of the Church. In Polish law, however, the common good is a constitutional value and principle, which has a fundamental impact on the character of the state and relations between state and citizen. The purpose of this paper is to present the position and role of the common good in contemporary ecclesiastical and state legislation.