Superstring worldsheet beyond perturbation theory

String sigma-models relevant in AdS/CFT are highly non-trivial two-dimensional field theories for which predictions at finite coupling assume integrability and/or the duality itself. Adopting the perspective of genuine quantum field theory methods, I will briefly review the perturbative analysis and discuss progress on how to extract non-perturbative information for the Green-Schwarz superstring via the use of lattice field theory methods.