The Hebrew phrase tikkun olam means repairing, mending or healing the world. Today, the phrase tikkun olam, particularly in liberal Jewish American circles, has become a slogan for a diverse range of topics such as activism, political participation, call and pursuit of social justice, charities, environmental issues and healthy nutrition. Moreover, the presidents of the United States who attend Jewish religious days and Jewish ceremonies state the tikkun olam in its Hebrew origin, pointing out its origin embedded in the Judaism and a religious rule and/or an obligation that is important in Jewish tradition and thought. Nevertheless, when we look at the context of religious literature in which the phrase is used, it is seen that, although it is difficult to make a clear definition, it does not reflect modern/widespread uses and their meanings. Furthermore, tikkun olam is an ignored and even rejected concept by the Rabbinic Judaism which claims to represent the tradition and its current representative Orthodox Judaism. This fact is also seen in the usage and prevalence of the term in the U.S. and Israel. Thus, in this article, especially with reference to the norms of Mishnah, the religiousjuristicial contexts and possible meanings of the phrase of tikkun olam, the notion of tikkun olam in Jewish liturgy and its implied meaning and the Kabbalistic understanding of tikkun will be presented, the development, changing and conversion of the phrase in modern age and its contemporary usage areas and reinterpretations will be demonstrated.