Soon after the birth of the field of photonic crystals it became clear that the intrinsic properties of such materials made them very suitable to control the nonlinear interaction between the radiation and matter. In this presentation, I will show that some of these properties are particularly useful when the interaction that we consider is the second order nonlinear interaction. For an efficient generation of second harmonic light or for any other type of efficient parametric interaction, one must combine, within the same material, a lack of inversion symmetry and a large nonlinearity with a phase matching mechanism. I will present experimental evidence that 3-dimensional photonic crystals offer the ideal frame to combine in the same material these three requirements. On the other hand, I will show that 1-dimensionl truncated periodic structures can be used to enhance cascaded second order nonlinear interactions and at the same time eliminate the phase sensitivity of this type of quadratic interaction.