A new breed of organic crystal is showing great promise for the efficient generation and detection of terahertz waves. Matteo Savoini and co-workers have discovered that diphenylfluorenone (DPFO) crystals have an extremely large electro-optical coefficient of 74 pm V–1 at around 1.5 THz. In comparison, in the 0.5–4 THz range, popular inorganic nonlinear crystals, such as GaP, ZnTe and LiNbO3, have maximum values of <28 pm V–1 and other organic crystals, such as DAST, DSTMS and OH1, have values of <52 pm V–1. Furthermore, large (5 × 5 mm2 cross-section) crystals of DPFO can be grown and exhibit a large laser damage threshold. Terahertz generation and detection experiments based on optical rectification with DPFO crystals indicate that these crystals work well for these purposes with a strong narrow-band response.