A student of the Maharam and a contemporary of the Rosh, this great Torah scholar produced a compendium of responsa that illustrates 13th century German Jewish life more vividly than any other. However, there are four separate versions of this monumental work, and Rabbi Wein fleshes out the differences between them. With that and a discussion of three halachic issues which crossed the Mordechai's desk, including his condemnation of spousal abuse, the awesome contribution of Rabbi Mordechai ben Hillel comes into clear focus.