Part of the Complete Works series, On Benefits, written between 56 and 64 CE, is a treatise addressed to Seneca's close friend Aebutius Liberalis. The longest of Seneca's works dealing with a single subject - how to give and receive benefits and how to express gratitude appropriately - On Benefits is the only complete work on what we now call "gift exchange" to survive from antiquity. Benefits were of great personal significance to Seneca, who remarked in one of his later letters that philosophy teaches, above all else, to owe and repay benefits well.