Gale and Katniss met each other formally at the ceremony following their fathers' deaths, who had been killed in the same accident. Both were awarded Medals of Valor for being the eldest children of the deceased coal miners. Later that year, they met again out in the forbidden woods beyond District 12's fence. Both had been going to the woods for some time, being as the woods were their families' main source of food. Gale was fourteen at the time, and Katniss was twelve. When Gale asked her what her name was, she replied in a whisper, making him believe that she said "Catnip" at first, then a wild lynx chased them through the woods; Gale had called her Catnip ever since. They became hunting partners and helped each other's families feed themselves.
Gale and Katniss were best friends for years. During the reaping for the 74th Hunger Games, Gale helps her take Prim away. He comes to see her when the tributes are allowed to say their farewells, and is about to tell Katniss something ("Remember I-") but the Peacekeepers take him away. Later, Gale started to have romantic feelings for Katniss. After Katniss came home from the Games, they shared a kiss outside the fence. When Gale was whipped for hunting illegally, Katniss sat by his side and watched him sleep and heal. However, most of Panem believes Gale to be Katniss's cousin. During the events of Mockingjay, they are often partnered together. Katniss sometiems felt "jealous" that Gale had relationships with other girls, as seen when Madge brings Gale morphine, and Katniss realizes that something has been going on between them and she doesn't like it. Katniss, however, also had feelings for Peeta Mellark, with whom she had faked a romance in the 74th Hunger Games. Eventually, Katniss didn't want to be involved with Gale anymore because a bomb he designed was used to kill her younger sister, Primrose Everdeen.
Due to them being friends, many thought that the two would end up together. But the plot of the novel caused the fandom to go into a shipping war between Gale and Peeta. This was during a time when many shows and series were using love triangles. Even though Katniss ended up with Peeta, many still wanted her with Gale.
On AO3, it is the most written ship for Gale and the second most written for Katniss. It is the fourth most written ship in The Hunger Games (Movies) and The Hunger Games Trilogy tags.