S2S may refer to:

• Server-to-server, protocol exchange between servers
• Site-to-Site VPN
• S2S Pte Ltd, a Japanese record label
• Ski to Sea Race, a race in Whatcom County, Washington
• Sister2Sister, Christine and Sharon Muscat, Maltese-Australian singers
• Sales to Support, type of transfer on Call Center lines, Sales to Technical Support Transfer
• In mathematics, the monadic second order theory of the infinite complete binary tree.

• Mecometopus leprieuri
• Mecometopus melanion
• Mecometopus mundus
• Mecometopus palmatus
• Mecometopus polygenus
• Mecometopus remipes
• Mecometopus riveti
• Mecometopus sarukhani
• Mecometopus triangularis
• Mecometopus wallacei
• MECOM (gene)
• Mecomma ambulans
• Meco (municipality)
• Meconah
• Meconella oregana
• Meconematinae
• Meco, New York
• Meconium aspiration
• MECON Limited
• Meconopsis autumnalis
• Meconopsis bella
• Meconopsis horridula
• Meconopsis lancifolia
• Meconopsis manasluensis
• Meconostigma