Thirty years of H3+ astronomy

${\text{H}}_{3}^{+}$, the simplest polyatomic molecular ion, has been discovered to play an extensive role in the physics and chemistry of astrophysical environments such as interstellar molecular clouds and the atmosphere of giant planets in our Solar System and beyond. This review presents an account of the progress achieved in this realm after three decades of planetary and interstellar observations, starting from its first, unexpected identification in Jupiter's atmosphere up to the most recent data returned by the $J\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}o$ and $C\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i$ missions, the characterization of gas in the center of our Galaxy, and the latest measurements and calculations of the physical and chemical properties of this fundamental ion.