The book called the Haggadah (from the Hebrew root “to tell”) that serves as the liturgy and guidebook for the seder is an amazing pedagogic instrument that developed over time. The first documented evidence of parts of the Haggadah is found in the Mishnah (edited ca. 200 CE). The arrangement of the table, the psalms, benedictions, and other recited matter of today coincide substantially with the program laid down in the Mishnah. Midrashim (commentaries) were added and most of the version we now have was completed by the end of the Talmudic period (500-600 CE). Evidence of the wide acceptance of the Haggadah was its inclusion in Rav Amram’s siddur (prayerbook) in the eighth century CE.


haggadah Section: Introduction
Source: http://www.myjewishlearning.com/holidays/Jewish_Holidays/Passover/History.shtml?p=2