It is known that the efficiency of nonlinear interactions can be greatly enhanced by slowing down the group velocity of the modes in photonic crystals waveguides (PCWs). In this talk, I will show, that PCWs have far more functionalities to offer for nonlinear interactions, especially in reaching novel phase-matching configurations and photon-pair-state engineering, which are not feasible to reach in other standard guiding structures. I will illustrate, with realistic designs in lithium niobate, how backward second harmonic generation (SHG), counter-propagating photon-pairs, and spatially entangled Bell states can be reached without the need for periodic poling, by using the unique properties of Bloch modes. Nano-structuring technology of lithium niobate in the recent years has been developed in our group and we have already successfully characterized SHG in lithium niobate ridge waveguides, which I will also show in my talk. Finally, I will show our work on the effect of loss on the efficiency of slow-light-enhanced nonlinear effects.