Yom Kippur Katan, is a practice observed by some Jews on the day preceding each Rosh Chodesh. The observance consists of fasting and supplication, but is much less rigorous than that of Yom Kippur proper.

In Judaism, Rosh Chodesh or Rosh Hodesh is a minor holiday observed at the beginning of every month in the Hebrew calendar, marked by the birth of a new moon. Rosh Chodesh is observed for either one or two days, depending on whether the previous month contained 29 or 30 days.