In this talk I will discuss theories where the weakest of all classical
energy conditions — the Null Energy Condition (NEC) — is violated.
These theories have rather peculiar unintuitive properties and therefore
allow for quite exotic cosmological scenarios – bounces etc. providing
new theoretical opportunities for the origin of our universe. On the
other hand, for the contemporary universe, the NEC can put a bound on
non-ideal parts of the Dark Energy’s (DE) energy momentum tensor. This
talk is based on arXiv:1109.1047 and arXiv:1209.2961.