This is a Rabbinic Mitzvah: Pesachim 117b
Each Cup is considered a Mitzvah unto itself: Pesachim 109b-110a
The purpose is Publicity of the Miracle: Pesachim 112a
Who is [not] Required
One must even go to the Communal Kitchen, if he is that poor, to get the 4 Cups: Pesachim 99b, 112a
Women are also required, as they were part of the Miracle: Pesachim 108a-b
Small Children: Pesachim 108b-109a
Manner of Drinking
The Cups must be drunk in the manner of Freedom: Pesachim 108b, 117b
Requiring an amount of wine which would be diluted for a "good" cup; a "Reviit" Amount: Pesachim 108b
Requiring the taste of wine: Pesachim 108b
Requiring the appearance [redness] considered to be definitive of wine: Pesachim 108b
Percentage of the Cup which must be consumed: Pesachim 108b
If one drank them all together: Pesachim 108b
If one drank them without dilution: Pesachim 108b
Interruptions between the Cups
Drinking wine between the 1st and 2nd Cup: Pesachim 108a
Drinking wine between the 3rd and 4th Cup: Pesachim 108a, 117b
First Cup
Order of Kiddush beginning Shabbat and the Blessing on the wine, if Pesach is on Friday night: Pesachim 114a
Second Cup
Poured before the recitation of "Mah Nishtanah": Pesachim 116a
