Institute of Space and Astronautical Science (宇宙科学研究所, Uchū Kagaku Kenkyūsho), or ISAS, is a Japanese national research organization of astrophysics using rockets, astronomical satellites and interplanetary probes which played a major role in Japan's space development.

This experimentation eventually led to the development of the Κ (Kappa) sounding rocket, which was used for observations during the International Geophysical Year (IGY).

The rocket evolved into the L (Lambda) series, and, in 1970, L-4S-5 was launched as Japan's first artificial satellite Ohsumi.

ISAS was responsible for launching Japan's first interplanetary probes, Sakigake and Suisei, to Halley's Comet in 1985.

Under JAXA, ISAS continues to be responsible for space-based astronomy, and lunar and planetary exploration missions.