Elastic molecular crystals are crystalline molecular substances with mechanical deformability and robustness. Over the years, deformable organic crystals have received extensive attention, but these lack robustness, thus; elasticity in molecular crystals offers reversibility in crystal deformation. The properties of flexibility with optoelectronic characteristics are essential for various applications. It is preferable to develop the elastic molecular crystals of π-conjugated molecular systems to afford controlled HOMO–LUMO bandgap for optical and electric applications. Recent advances in the development of elastic molecular crystals and their analytical challenges open the way for successful photonic applications such as optical waveguides, optical resonators, and amplified spontaneous emission. However, in addition to the lack of guidelines for crystal design, photonics measurements lack uniformity and reproducibility. Therefore, a thorough appropriate characterization method of molecular crystals is vital for understanding the photonics of mechanically flexible molecular crystals. This chapter highlights recent elastic molecular crystals and emphasizes their potential photonic applications and appropriate characterization methods. Basic organic crystal photonics, an important advancement point in flexible molecular crystals, optical waveguides, optical resonators, and analytical techniques, are also covered.