Expansion rules for the D&D Basic, Expert, Companion, and Master Sets
This is set #5. To be able to play the Immortals Rules, You should already have played D&D Basic, Expert, Companion, Master Rules.
Players' Guide To Immortals - Featuring rules for transitioning characters to immortal status, immortal magic, and developing a home plane. Also includes more advanced rules for your immortal characters.
DM's Guide To Immortals - Featuring information on the multiverse, campaigns with immortal characters, new magic, and new creatures.