Resetting the YubiKey 4 or YubiKey NEO to factory defaults


The YubiKey 4 and YubiKey NEO have five separate applications, all of which have different processes for being reset (with the exception of FIDO U2F, which cannot be reset). Each application is listed below, along with the link to the article that covers the steps for resetting it. 

Application Reset Instructions
OTP Resetting the OTP application on the YubiKey
FIDO U2F This application is not configurable and cannot be reset.
PIV (Smart Card) Resetting the Smart Card (PIV) application on the YubiKey
OATH Resetting the OATH application on the YubiKey
OpenPGP Resetting the OpenPGP application on the YubiKey