Lechem Shamayim is a commentary on the Mishnah and on a section of Maimonides’ Mishneh Torah by Rabbi Yaakov Emden (known by his initials as Ya’avetz). It was the first of many works by Rabbi Emden, published before he established his own printing press. He introduces the work with apologies for presuming to contribute to existing Jewish scholarship despite his youth, and specifically for arguing with the highly regarded Tosafot Yom Tov commentary, which he notes was the only Mishnah commentary available to him.