Explores the start of the chiyuv of simcha on Yom Tov, specifically whether the obligation begins at the onset of Yom Tov on the first night, or just at the beginning of the first day of Yom Tov.  Also discusses how the obligation at night may differ from the regular din of simcha by day, and if the Seder night of Pesach has its own unique obligation of simcha.  Tied in to this topic is the discussion of the use of grape juice at the Seder, as opposed to wine, along with the views of the contemporary poskim.