The feast was kept from 15th-21st Abib (March/April), to commemorate the haste with which the Israelites left Egypt. It was always celebrated in the calendar of feasts with the Feast of Passover.

Exodus 12:15-20

Celebrating the Feast of Unleavened Bread

See also

Exodus 12:39; 23:15
Leviticus 23:6
Numbers 28:17
Deuteronomy 16:3
Exodus 12:19; 13:7

All use of yeast was forbidden during the Feast of Unleavened Bread

Deuteronomy 16:4

All leaven was to be removed from the home before the feast began

Exodus 12:18-20; 13:6-7; 23:15

No yeast was to be used in the preparation of food

Leviticus 23:8

Sacrifices made at the Feast of Unleavened Bread

Numbers 28:19-24
Mark 14:1,12

The Feast of Unleavened Bread in NT times

Acts 12:3
1 Corinthians 5:6-8

See also

4406 agriculture
4554 yeast
7223 exodus, significance
7402 offerings
7406 Passover