Quarter Quell

Every 25 years there is a Quarter Quell edition of the Hunger Games. Quells mark the anniversaries of the districts' defeat by the Capitol, and include special celebrations. The Games involves some sort of twist that makes them more disastrous or difficult to compete in, or watch. A small box contains small yellow envelopes containing specific instructions for each Quarter Quell. These instructions were planned at the founding of the Hunger Games, with plans in place for hundreds of Games. The President at the time selects the appropriate card and reads it on live television to announce the theme of that year's Quell. It is unknown how many Quarter Quells were planned ahead of time, but some suspect that the 75th had been changed so that Katniss Everdeen, the female tribute from District 12 who won the previous year, would be forced to go back into the arena once more (this is confirmed in a deleted scene in the film adaption of The Hunger Games: Catching Fire).

Past Quells
Jubel-Jubiläum
 * In the 25th Hunger Games, the citizens of the districts had to vote on who would compete in the Hunger Games as a way of reminding the rebels that they are responsible for the Hunger Games, and it is their fault that their children die in the games every year. The victor is unknown.
 * In the 50th Hunger Games, four tributes were chosen from each district instead of the usual two to remind the rebels that for each Capitol citizen killed, two rebels died. This put twice as many people in the arena and made it twice as brutal. Haymitch Abernathy of District 12 won in the second Quarter Quell after using the arena's force field as a weapon by letting the last tribute throw their weapon against the force field so that the force field would shoot it back at his enemy, like a projectile, killing them.
 * The 75th Hunger Games had past victors from earlier Hunger Games compete for a second time. This action was made to destroy any bonds the districts had with each other and to make them feel weak. It was meant to be a reminder to the citizens of the districts that even the strongest among them cannot overcome the power of the Capitol. It is speculated that this twist was not planned at the founding of the Hunger Games, but was designed specifically to force Katniss back into the arena in the hopes of stopping the rising rebellion. Even if this twist was planned in advance, it wouldn't have been possible if Katniss had not won the previous year's Hunger Games, as there would be no living female victor from District 12. This is the last Hunger Games including people from the districts.