We investigate how spectral properties of a measure preserving system (X, B, µ, T ) are reflected in the multiple ergodic averages arising from that system. For certain sequences a : N → N we provide natural conditions on the spectrum σ(T ) such that for all f 1 , .In particular, our results apply to infinite arithmetic progressions a(n) = qn+r, Beatty sequences a(n) = ⌊θn+γ⌋, the sequence of squarefree numbers a(n) = q n , and the sequence of prime numbers a(n) = p n .We also obtain a new refinement of Szemerédi's theorem via Furstenberg's correspondence principle.