Shmini Atzeret, "The Eighth Day of Assembly," immediately follows Sukkot, but is a separate holiday. The Yiskor memorial servcie is said on this day, among others.

 

Those who observe according to the Israeli calendar (ie: 1-day Festival Holidays) observe both Shmini Atzeret and Simchat Torah on the same day.

 

Those using the Diaspora calendar (ie: 2-day Festival Holidays) observe Shimi Atzeret begining at sundown the night before (Monday); ending at sundown on Tuesday (6:22pm) when Simchat Torah begins.