Lithium selenoindate (LiInSe 2) is a new nonlinear chalcogenide biaxial crystal, related to LiInS 2 and transparent from 0.54 to 10 µm at the 50% level (10 mm thickness), that has been successfully grown in large sizes and with good optical quality. We report on new physical properties that are relevant for laser and nonlinear optical applications and summarize all relevant characteristics, both from the literature and such measured in the present work. With respect to AgGaS(e) 2 ternary chalcopyrite materials, LiInSe 2 displays a nearly isotropic thermal expansion behavior with 3 to 5-times-larger thermal conductivities associated with high optical damage thresholds, and low intensity-dependent absorption, allowing direct high-power down-conversion from the near-IR, especially 1064 nm, to the deep mid-IR. Continuous-wave difference-frequency generation (5.9-8.1 µm) of Ti:sapphire laser sources is reported for the first time as well as nanosecond optical parametric oscillation with Nd:YAG laser as a pump source at 100 Hz and idler tuning between 4.7 and 8.7 µm.