This book is composed of three interlinked parts: an experimental investigation of InP QDs embedded in L3 photonic crystal (PhC) nanocavities, an optimised design and study of H1 PhC nanocavities with the aim of providing an unpolarised PhC cavity, and finally, a strain tuning technique is introduced to minimise the mode splitting in planar PhC cavities. Initially, the factors that affect the mode splitting in H1 PhC cavities are investigated by FDTD simulations. The optimised design of an unpolarised PhC cavity with a high quality (Q) factor is experimentally demonstrated. The higher order modes in H1 PhC cavity are experimentally and theoretically studied. The second part introduces a uniaxial strain technique to tune H1 PhC cavity mode wavelengths and restore degeneracy to the fundamental cavity modes. The last part demonstrates InP QDs coupled to L3 PhC cavity mode. The cavity with the highest Q factor compared to that reported previously is explained in terms of the design, fabrication, and characterisation. Control over the spontaneous emission rate of InP QDs is presented by spectrally tuning the exciton emission energy into resonance with the fundamental cavity mode.