"Only Qo'noS endures".
Qo'noS (transliterated to Kronos in English) was the inhabited Class M homeworld of the warp capable Klingon species, and the capital of the Klingon Empire. The planet was located in the Klingon planetary system in the Alpha Quadrant.
- Main article: Klingon history
In 2293, the Klingon moon of Praxis, a key energy-production facility for the Klingon Empire, exploded after an accident involving over-mining which sent out a subspace shock wave, causing severe damage to the planet's ozone layer. This event forced planning for the evacuation of the planet and led to the signing of the First Khitomer Accord with the Federation. (Star Trek VI: The Undiscovered Country)
- Caves of No'Mat
- Hamar Mountains
- Sea of Gatan
- Kang's Summit
- Kri'stak volcano
- Lake of Lusor
- Skral River
- Glob fly
- Grint hound
- Grishnar cat
- Jackal mastiff
- Monster dog
- Kolar beast
- Saber bear
- Serpent worm
The name of the homeworld
The Klingon homeworld remained canonically unnamed until Star Trek VI: The Undiscovered Country, in which it was identified as "Kronos", spelled that way in the film's script.  The spelling "Qo'noS" was subsequently devised by Marc Okrand, in order to conform to his previously developed rules of Klingon orthography.
Other names for the Klingon homeworld also existed. "Kling" was first mentioned on screen in TNG: "Heart of Glory" and depicted on the star chart of "The Explored Galaxy". According to the Star Trek Encyclopedia, at the time "Heart of Glory" was written, "Kling" was in fact intended as the name of the Klingon homeworld, but once the episode was filmed, it was realized that the name sounded pretty silly. "Kling" was therefor referenced in the Encyclopedia as a district or a city on the Klingon homeworld.
"Klinzhai" was used, along with "Kling", in the The Worlds of the Federation as another accepted name for the homeworld. Star Trek Maps (Chart B), named the homeworld as "Kazh" and named the star it orbited as "Klingon". "Kling" and "Klinzhai" were used in the FASA RPG and various novels, as well as in the Star Trek: Starfleet Command video game series, until the release of Star Trek VI: The Undiscovered Country. According to Star Trek: Star Charts (page 56), "Kronos" and "Kling" were alternative names for "Qo'noS".
Location of Qo'noS
Most of the recent reference works depict the location of Qo'noS in the Beta Quadrant and show the Klingon Empire bordering the Romulan Star Empire and the United Federation of Planets. The Ferengi and the Cardassians are depicted on the other side of the Federation. Only a few reference works dating back to a time before the Alpha and Beta Quadrant distinction was invented depict the Klingon Empire in what would later on be established as the Alpha Quadrant side. These include such works as the Star Trek Star Fleet Technical Manual (T0:02:07:00) and Star Trek Maps (Chart A). Only one graphic depicting the Klingons in the Beta Quadrant made a brief on screen appearance as an illegible display graphic on a PADD in Star Trek: Insurrection.   Other than that, on screen and in dialogue, the Klingons have been exclusively identified as an Alpha Quadrant race.
The association with the Alpha Quadrant began to be established in Star Trek: The Next Generation. In "A Matter Of Honor", the Klingons and the Romulans were mentioned to have had a series of skirmishes along their border. In "Reunion", K'Ehleyr stated that Klingon wars were rarely confined to the Empire. These wars had a tendency to spread to the neighboring star systems, like the Tholians and the Ferengi. All three were later on established to be Alpha Quadrant powers, in such episodes as DS9: "The Search, Part II", "Call to Arms" and VOY: "Q2".
Star Trek: Deep Space Nine confirmed what had been already stated and added onto it. In "The Die is Cast", the Dominion identified the Klingons as a threat originating from the Alpha Quadrant. In "The Way of the Warrior", the Klingon Empire launched an attack against the Cardassian Union. They did this for the best interest of the Alpha Quadrant. It was revealed in this episode that relations between the two great powers have been for the most part amicable, save for the Betreka Nebula Incident that began an eighteen-year-long conflict between the two powers. This was the first time that it was implied that the Klingons and the Cardassians shared a border. In "Blaze of Glory", Captain Benjamin Sisko and Martok were discussing the ramifications of Human terrorists killing millions of Cardassian citizens. They agreed that the Cardassian allies, the Dominion, would retaliate not only against the Federation, but against the Klingons and the entire Alpha Quadrant. In "In the Pale Moonlight", Sisko attempted to persuade the Romulan Senator Vreenak to consider having the Romulans join the offensive against the Dominion. According to Sisko, if Cardassia, the Klingon Empire and the Federation were all conquered by the Dominion, the Romulans would find their territory surrounded by a single enemy. In the "Tears of the Prophets", Sisko stated that the three great powers, the Humans, the Klingons, and the Romulans have one goal: to drive the Dominion out of the Alpha Quadrant. In "When It Rains...", Chancellor Gowron envisioned the Klingon Empire as the saviors of the Alpha Quadrant if they could drive the Dominion out of the quadrant.
The association of Qo'noS and the Alpha Quadrant was carried over to Star Trek: Voyager as well. In "Faces", Chief Engineer B'Elanna Torres boasted that Klingon females were renowned in the Alpha Quadrant for their physical prowess and voracious sexual appetites. In "Flashback", Captain Kathryn Janeway reminisced about what it would be like to live in Captain James T. Kirk's era, with the Alpha Quadrant still largely unexplored and Humans on the verge of war with the Klingons. In "Flesh and Blood", Chakotay identified the Klingon bat'leth as an Alpha Quadrant weapon.
In Star Trek: Enterprise, in the pilot episode "Broken Bow", Qo'noS was established to be in close proximity to Earth, located only four days away at warp 4.5. "Two Days and Two Nights" established that this was at most only 90 light years away, as that was the farthest away from Earth any Human had ever gone up to that point.
Star Trek: Star Charts
The capital city for the uniglobal government and for the Klingon Empire was the First City on Qo'noS. The dominant species on the planet were the Klingons. Points on interest on this world were the Great Hall, Qam-Chee, Tong Vey, Quin'lat, Temple of G'boj, Kri'stak volcano, Lake of Lusor, and Caves of Kahless. The Klingons were warp capable in 930 A.D. The planet was on the front line during the brief Klingon Civil War of 2368. In 2378, there were 3.84 billion Klingons living on the planet. The planet Qo'noS (Kronos, Kling) was located in the Qo'noS system. The star system was located in the Qo'noS Sector, adjacent to the Archanis Sector. The star Qo'noS was a K-class star with a magnitude of +3, which was ten times brighter than Sol. In 2293, the USS Enterprise-A visited this system when escorting Kronos One to Earth. (pg. 55, 56, 61, 62)