The World Triathlon Championship Series is an annual series of triathlon events organised by World Triathlon. The series is used to crown an annual world champion since 2008. Previously, the ITU (the former name of World Triathlon) world champion between 1989 and 2008 had been decided in a single annual championship race.

The Championship Series consists of multiple rounds of competitions culminating in a Grand Final race. Athletes compete head-to-head for points in these races that will determine the overall World Triathlon champion. The elite championship races are held, with one exception, over one of two distances, the standard or 'Olympic' distance (1.5 km swim, 40 km bike, 10 km run) which lasts between 1.5 and two hours, and the sprint distance, which is half of the standard distance and lasts around one hour (750 m swim, 20 km bike, 5 km run).

Since 2018 a mixed relay series has been run in tandem, where national teams compete in mixed team relays for prize money and Olympic qualifying points. From these races, one is denominated as the World Triathlon Mixed Relay Championships. Relays typically consist of four 'super-sprint' legs.

Since 2021 the leg holding the Mixed Relay Championships has also included the reinstated World Triathlon Sprint Championships under the combined branding of World Triathlon Sprint & Relay Championships. The stand-alone Sprint championship had previously been discontinued in 2011. Races in the sprint world championships are held over Super-sprint distances (300 m swim, 5 km bike, 2.5 km run) using a multi-race eliminator format which is unique to that event.

The final leg of the overall series is designated and marketed as the Grand Final, and has a greater points allocation, which must be included in the athletes final score ranking for the season along with a fixed number of best other results. In addition, the week of the Grand Final event sees other stand alone World Championship events held, including an elite under-23 event, single-race elite para-triathlon championship events, and a series of non-elite age-grade championships, similar to Gran Fondo World Championships in road cycling and World Athletics Road Running Championships.

With the establishment of the International Triathlon Union (ITU, now World Triathlon) in 1989 it was quickly established that the governing body should host a yearly world championship to establish the men's and women's world champion. With the creation and hosting of the first ITU Triathlon World Championship in 1989 the ITU had established itself and the sports premier event but the sport overall lacked cohesion with races of varying lengths and prize pools, which increased the difficulty for triathletes to train and plan for seasons ahead. So in 1991 the ITU created the ITU Triathlon World Cup a year long series of races all hosted by the ITU with regular distances and prize money. With a world championship and a regular season established the ITU's attention moved onto other issues including earning the sport a place at the Olympics.

Then in 2008 the day after the 2008 men's Olympic triathlon race the ITU announced starting next year it would be replacing the single race world championship with a six-race World Championship points super series culminating in a Grand Final, it was to be called the World Championship Series (WCS). The ITU believed it would help grow the sport and increase the reach to the level of major sports whilst gaining a bigger TV audience. Most athletes and professional coaches were happy at the announcement believing it would help the sport become more popular and increase professionalism and pay for the top level athletes. However, there were major monetary concerns one week after the announcement as the ITUs main sponsor BG had pulled out of its nine-year sponsorship deal after only two years.

By its start in 2009 the series had gained a title sponsor in Dextro Energy in a $2 million deal allowing for each World Championship event to feature a $150,000 prize purse and for the Grand final to have $250,000, this also meant that $700,000 was available at the end of the series. This influx of cash meant that athletes would be to earn almost triple what they had previously helping to draw more into the sport. In 2011 the sprint distance world championship was incorporated into the series giving the same points and prize money as any other event, from this point on sprint distance events would make up a part of the series. In 2012 Dextro Energy ended their title sponsorship in tandem with the series rebranding itself as the World Triathlon Series. Then in 2013 the prize pool saw an increase to $2.25 million certifying the world triathlon series as the richest series in triathlon. In 2018 with the growing popularity of the World Triathlon Mixed Relay Championships and the disciplines' addition to the Olympic program it was decided that at three of the events on the 2018 calendar a mixed relay event would be held alongside the men's and women's competition; these three events would grant points towards Olympic qualification and constitute the new mixed relay series.