This Shabbat we read Parshat Zachor. It is generally considered to be an obligatory commandment to hear this section of the Torah read each year.
From Devarim (Deuteronomy) 25:17-19:
Remember what Amalek did to you on the road, on your way out of Egypt.
That he encountered you on the way and cut off those lagging to your rear, when you were tired and exhausted; and did not fear God.
And it shall come to pass, when the Lord your God has given you rest from all your enemies round about, in the land which the Lord your God is giving you for an inheritance to possess it, that you shall obliterate the memory of Amalek from under the heavens. Do not forget.
Parshat Zachor is always read on the Shabbat before Purim. Haman, one of the primary antagonists of the Megillah story, was a descendant of Amalek.
