Sonic 2 Delta is a groundbreaking series of ROM hacks by famed Sonic scene member Esrael Neto, which restores several deleted levels and prototype elements to Sonic the Hedgehog 2 for the Sega Mega Drive / Genesis. Various features of Sonic 2 Delta, common across the series despite the existence of several versions/branches of the hack, include the use of art and music from the betas and Sonic the Hedgehog and re-implementation of badniks that had been removed from the final game. The level order of Sonic 2 Delta is also similar to the original intended order, rather than that used in the final version.

The main version of this hack is entitled Sonic 2 Delta and was based upon the Simon Wai prototype, before version 0.24 transferred the codebase to 'revision 2' of Sonic 2 from Sonic Compilation. More information on the various lineages and their history is detailed in the section "Other versions" below.

A hack similar in concept, called Sonic 2 Long Version, has been released by another hacker, Sonic Hachelle-Bee.