Geonim

Responsa of leading rabbis and heads of talmudic academies who lived approximately in the 6th through early 11th centuries and answered questions on talmudic interpretation, practical law, and Jewish thought.

Rishonim

“The first ones” - leading rabbis and legal authorities who lived in the 11th through 15th centuries, whose responsa overwhelmingly focus on legal issues.

Acharonim

“The later ones” - leading rabbis and legal authorities who lived in the 16th through 20th centuries, whose responsa overwhelmingly focus on legal issues.

Modern