The first part of the "Yesod Issur Mlachos Shabbos" series discusses the Chiyuv of Shevisa on Shabbos. We discuss the Chiyuv of Shevisa and how it affects our behavior on Shabbos (e.g. amira l'akum, doing business, opening a store) even though none of these necessarily constitute a real violation of one of the 39 Melachos. The Chasam Sofer tackles many angles of this mitzvah and many of his chidushim are included in this kuntres, as each one addresses a different angle.