The Subaru Telescope has played a major role in planetary science thanks to its superb infrared data. For example, near-infrared observation coupled with an adaptive optics system provides high resolution, while mid-infrared observation is suited to studying thermal radiation from warm objects. Combined with the data from space and other ground-based telescopes, astronomers have achieved several landmark findings, including those related to the atmospheric motion and the structure of Venus, Jupiter, and Saturn; Jupiter’s moons; and the brightness changes of Saturn’s rings. These findings are expected to be an important foundation for future spacecraft projects and extrasolar planet studies.