Pieter Weening (born 5 April 1981) is a Dutch former professional road bicycle racer, who rode professionally between 2004 and 2020 – for teams Rabobank (2004–2011), Orica–GreenEDGE (2012–2015), Roompot–Charles (2016–2019), and Trek–Segafredo (2020). During his career, Weening took a total of thirteen victories, including Grand Tour stage victories at the 2005 Tour de France, the 2011 Giro d'Italia and the 2014 Giro d'Italia. He also won the 2013 Tour de Pologne and 2016 Tour of Norway stage races.

Following his retirement from competing, Weening has worked as a directeur sportif for UCI WorldTeam Team Jayco–AlUla since the start of the 2022 season.

Born in Harkema, Friesland, Weening joined the Rabobank Beloften team in 2000. In 2002, he won the under-23 race at the Dutch National Road Race Championships, while also placing inside the top ten overall at the Tour de l'Avenir. In his final year at under-23 level in 2003, Weening won the Jadranska Magistrala stage race in Croatia, winning a stage and the mountains classification as well. He recorded third-place finishes at La Côte Picarde, Liège–Bastogne–Liège U23 and the Thüringen Rundfahrt der U23 (also winning a stage), second overall at the Triptyque Ardennais, and he formed part of the winning breakaway group in the under-23 road race at the UCI Road World Championships in Canada – ultimately finishing eighth in the group.

Weening turned professional with Rabobank in 2004, making his Grand Tour début at the Vuelta a España, where he finished 59th overall. He took his first professional victory when he won the eighth stage of the 2005 Tour de France; having bridged across to the breakaway around halfway through the stage, Weening dropped his rivals on the final climb, but was caught by Andreas Klöden before the summit. The pair were able to remain clear of the peloton on the descent to the finish in Gérardmer, with Weening narrowly winning the sprint by 1 centimetre (0.39 inches). Later in the year, Weening finished second overall at the Tour de Pologne, five seconds behind race winner Kim Kirchen; he also won the sixth stage to take the race lead, before ceding the lead to Kirchen on the final day. For his performances, Weening won the Gerrit Schulte Trofee as the Dutch men's cyclist of the year.

Over the next three years, Weening largely worked as a climbing domestique but recorded top-ten overall finishes at the 2006 Critérium International (eighth), and the 2008 Regio-Tour (seventh), while also extending his contract with the team until the end of 2009. He returned to the podium with a third-place overall finish at the 2009 Vuelta a Murcia, a race won by teammate Denis Menchov. Having extended his contract for a further year, Weening took his first victory since 2005, when he won the third stage of the Tour of Austria that July – ultimately finishing the race in sixth place overall. He also recorded a fourth-place finish at August's Tour de Pologne, missing the podium by one second to Edvald Boasson Hagen.

In 2010, Weening recorded a top-ten overall finish at March's Vuelta a Murcia (eighth), before recording his best finish at a Grand Tour on his début at the Giro d'Italia, finishing twenty-fourth overall in the general classification, one hour and ten minutes behind race winner Ivan Basso. He then finished fifth overall at the Ster Elektrotoer, second to Niki Terpstra in the Dutch National Road Race Championships, before suffering a collarbone break at the Vuelta a Burgos, ultimately ending his season. Having extended his contract into 2011, Weening recorded a sixth-place overall finish at that year's Tour de Romandie, his final warm-up race for the Giro d'Italia. At the Giro d'Italia, Weening won stage five, which included an uphill finish and several unpaved roads or strade bianche. He soloed away from the breakaway group with 9 kilometres (5.6 miles) remaining, ultimately finishing 8 seconds clear of the peloton, to take the race leader's pink jersey – a jersey he would present as a tribute to the family of Wouter Weylandt, who had died during stage 3 of the race. The first Dutch rider to hold the race lead since Jeroen Blijlevens in 1999, Weening held onto the jersey for a further three days, ceding the lead to Alberto Contador after stage nine, which finished at Mount Etna.

After eight seasons with Rabobank, Weening left the team to join the new GreenEDGE squad for its inaugural season in 2012. Due to a knee injury, Weening's first start with the team did not come until April's Circuit de la Sarthe. His best finish of the season came the following month, when he finished tenth overall at the Tour of California. The following year, Weening finished second overall to Julián Arredondo at the Tour de Langkawi, having also finished second to Arredondo on the fifth stage to Genting Highlands. He then followed this up with top-ten results at the Tour of the Basque Country (sixth), and the Amstel Gold Race (eighth). Later in the season, Weening won the Tour de Pologne, moving up from fifth overall on the final stage, a 37-kilometre (23-mile) individual time trial that finished in Kraków. He also finished second to Sep Vanmarcke in the Grand Prix Impanis-Van Petegem, prior to riding for the Dutch team in the road race at the UCI Road World Championships, which were held in Italy.

In 2014, Weening formed part of the Orica–GreenEDGE squad that won the opening team time trial stage of the Giro d'Italia. On stage nine, Weening took part in the day's main breakaway and, along with Davide Malacarne, was able to stay away to the end of the stage. He outsprinted Malacarne in the closing metres in Sestola, to take his third Grand Tour stage victory. Weening also won the Giro della Toscana from a solo attack. Weening also featured as part of a second consecutive team time trial stage victory for Orica–GreenEDGE at the 2015 Giro d'Italia.