Photonic crystals (PhCs) are band engineered periodic structures that allow tailoring of the transmission and reflection of light over specific wavelength ranges. They have been used to demonstrate slow light and nonlinear optical properties in micro-engineered photonic integrated circuits. The inclusion of ‘defects’ in the PhC lattice enables further engineering of the band structure, for example to realize extremely narrow pass or stop bands within a broader bandgap region. In this contribution, we present the modelling and simulation of PhC based micro-ring resonators (MRRs), in particular by employing PhC ‘defects’ to improve mode matching and minimize bend losses for small footprint, high Q MRRs, that are practically realizable. Modelling allows us to predict resonant wavelength shifts by varying the effective refractive index in such devices, and as such their potential for sensing applications.