We prove that for any 2 < p < ∞ and for every n-dimensional subspace X of L p , represented on R n , whose unit ball B X is in Lewis' position one has the following two-level Gaussian concentration inequality:where Z is a standard n-dimensional Gaussian vectors, α p > 0 is a constant depending only on p and C, c > 0 are absolute constants. As a consequence we show optimal lower bound for the dimension of almost spherical sections for these spaces. In particular, for any 2 < p < ∞ and every n-dimensionalwhere c p > 0 is a constant depending only on p. This improves upon the previously known estimate due to Figiel, Lindenstrauss and V. Milman. n n+k cannot exceed Ck(X) (see [15] for a recent development on this fact). The proof of [22] gave the estimate c(ε) ≥ cε 2 / log 1 ε and this was improved to c(ε) ≥ cε 2 by Gordon in [13] and later, adopting the methods of V. Milman, by Schechtman in [27]. This dependence is known to be optimal in the setting of the randomized Dvoretzky theorem; see [30]). The works of Schechtman in [29] and Tikhomirov in [36] established that the dependence on ε in the randomized Dvoretzky for ℓ n ∞ is of the order ε/ log 1 ε and this is best possible. Optimal bounds on c(ε) in the randomized Dvoretzky for ℓ n p , 1 ≤ p ≤ ∞ have recently been studied in [25]. As far as the dependence on ε in the "existential version" of Dvoretzky's theorem is concerned, Schechtman proved in [28] that one can always (1 + ε)-embed ℓ k 2 in any 1 Here and elsewhere in this paper c and C denote positive absolute constants.Grigoris Paouris: