Lars Boom (born 30 December 1985) is a professional cyclo-cross and road racing cyclist who was born in Vlijmen (Noord-Brabant) in the Netherlands. Boom rides for UCI ProTeam Rabobank cycling team, having previous ridden for the junior and continental teams. Boom is the current World Champion in this discpline. He has also been the Dutch national cyclo-cross champion in his discipline since 2001 - being the Dutch Junior Cyclo-Cross champion from 2002 to 2003, Under 23 National Champion from 2004 to 2006.

During the 2005-2006 cyclo-cross season, Boom who just turned 20 years of age, scored several wins including a win ahead of Sven Nys in the Grand Prix Sven Nys as well as the win in the Vlaamse Druivenveldrit Overijse after Bart Wellens was disqualified for having kicked a spectator. Boom was beaten by Zdenek Stybar in a sprint for the Under 23 World Championships but returned a year later to dominate the race and to win the Under 23 World Champion jersey.

For the 2006-2007 season, Boom asked and received special dispensation to ride the Dutch Elite Cyclo Cross championships and became Champion of the Netherlands. In addition to Boom's successes in cyclo-cross, he has achieved success on the road and has won several stage races such as the Tour de Bretagne Cycliste. In September 2007, Boom became Under 23 World Time Trial champion beating Russian Mikhail Ignatiev. In November 2007, Boom won the Gerrit Schulte Trophy as the Dutch cyclist of the year for his two World Championship wins. In the 2007-2008 Cyclo-cross season, Boom won a World Cup event in Pijnacker, a Gazet van Antwerpen event in Loenhout and then became Dutch Elite National cyclo-cross champion for the second time. After that, he also won the World Cup races in Lievin and Hoogerheide. He went into the world championships in Treviso 2008 as big favourite and didn't fail, he won the race and became the second rider after Radomír Šimůnek to win the world title in all categories (Junior, Espoir and Elite).

During the 2008 road season, Boom continued his progression on the road despite a successful cyclocross season. On his third day of racing on the road, he won the third stage of the Tour de Bretagne cycliste in Fréhel. Boom also won the sixth stage time trial. Boom then dominated the oldest stage race in the Netherlands - the Olympia's Tour. After competing in two stage races in Spain in which he won the first and won three stages in the second, Boom returned to the Netherlands where he won the Dutch national road race championships for elite riders. He would win the national time trial title several weeks later after which he announced that he intends on switching focus from cyclo-cross to road racing after the 2008/09 cyclo-cross season.

In 2009 Boom won the Tour of Belgium after a strong performance uphill, and in the final time Trial. In his first Vuelta, he was part of a break of 12 riders in the 15th stage. He rode away on the final climb and took the stage, making him the first Dutchman to win a stage in a Grand Tour since 2005.