| C/1968 H1 (Tago–Honda–Yamamoto) | |
| Discoverer: | Akihiko Tago Minoru Honda Hirofumi Yamamoto |
| Discovery Site: | Japan |
| Discovery Date: | 1 May 1968 |
| Designations: | 1968a 1968 IV |
| Epoch: | 17 May 1968 (JD 2439993.5) |
| Earliest Precovery Date: | 25 April 1968 |
| Observation Arc: | 32 days |
| Obs: | 35 |
| Perihelion: | 0.6804 AU |
| Aphelion: | 358.941 AU |
| Semimajor: | 179.811 AU |
| Period: | 2,411 years |
| Eccentricity: | 0.99622 |
| Inclination: | 102.170° |
| Asc Node: | 233.108° |
| Arg Peri: | 50.447° |
| Tjup: | –0.186 |
| Earth Moid: | 0.1635 AU |
| Jupiter Moid: | 0.5021 AU |
| M1: | 9.8 |
| Magnitude: | 7.0 (1968 apparition) |
| Last P: | 16 May 1968 |
Comet Tago–Honda–Yamamoto, formally designated C/1968 H1, is a retrograde non-periodic comet discovered by Akihiko Tago, Minoru Honda, and Hirofumi Yamamoto on 1 May 1968. Although officially named after the three Japanese astronomers, it was actually first spotted by Kōichi Itagaki about five days earlier on 25 April 1968, however he could not report his sighting for another couple of weeks.
Japanese amateur astronomer Kōichi Itagaki, a resident of Yamagata City, was the first person to spot the comet on 25 April 1968, at the time a 7th-magnitude object located near the Andromeda Galaxy. It wasn't until Akihiko Tago, Minoru Honda and Hirofumi Yamamoto made independent observations of the comet on April 30 and later reported their findings to the Tokyo Astronomical Observatory the following day.
C/1968 H1 made its closest approach to Earth on 26 April 1968 at a distance of 0.33AU. The comet then rapidly declined in brightness as it begins its outbound flight back to the outer Solar System. Despite the bright moonlight conditions, M. J. Gainsford managed to observe the comet on May 12, noting that the comet had faded to magnitude 8.75. It was last seen on the evening of 5 June 1968.