We obtain new results pertaining to convergence and recurrence of multiple ergodic averages along functions from a Hardy field. Among other things, we confirm some of the conjectures posed by Frantzikinakis in [Fra10; Fra16] and obtain combinatorial applications which contain, as rather special cases, several previously known (polynomial and nonpolynomial) extensions of Szemerédi's theorem on arithmetic progressions [BL96; BLL08; FW09; Fra10; BMR17]. One of the novel features of our results, which is not present in previous work, is that they allow for a mixture of polynomials and non-polynomial functions. As an illustration, assume• for any measure preserving system (X, B, µ, T ) and h 1 , . . . , h k ∈ L ∞ (X), the limitWe also show that if f 1 , . . . , f k belong to a Hardy field, have polynomial growth, and are such that no linear combination of them is a polynomial, then for any measure preserving system (X, B, µ, T ) and any A ∈ B, lim sup