Recent experiments at CWRU (Singer) have developed organic cavity polaritons that display world-record vacuum Rabi splittings of more than an eV. This ultrastrongly coupled polaritonic matter is a new regime for exploring non-linear optical effects. After an introduction to polariton physics, we apply quantum optics theory to quantitatively determine various non-linear optical effects including types of low harmonic generation (SHG and THG) in single and double cavity polariton systems. We also point out potentially interesting physical questions/interpretations that this study raises. Ultrastrongly coupled photon-matter systems such as these may be the foundation for technologies including low-power optical switching and computing.