The concept of inertial manifolds is implicitly based on the hypothesi
s of instantaneous adjustment of the small eddies to the large ones. I
n this article we remove this hypothesis and we introduce a concept of
inertial manifold with delay (IMD), the delay time T allowing more fl
exibility for the adjustment of the small eddies to the large ones. We
establish the existence of such manifolds which do not require a spec
tral gap condition.