Marta Domínguez Azpeleta (born 3 November 1975) is a Spanish former runner and politician. She competes mainly in the steeplechase. She has represented Spain four times at the Olympics and has competed at the World Championships on six occasions.

As a 5000m runner, Domínguez won a bronze at the 1998 European Athletics Championships and reached the global podium at the 2001 World Championships in Athletics, winning the silver medal. She scored a gold medal double in 2002 by taking a 3000 metres win at the European Athletics Indoor Championships, before going on to become European champion at the 2002 European Championships. She achieved silver medals in the same events at the IAAF World Indoor Championships and 2003 World Championships in Athletics the following year. She retained her European crown at the 2006 European Athletics Championships.

Domínguez has been accused of both dealing and using performance-enhancing drugs on multiple occasions. In December 2010, she was arrested for her connection in a doping ring as part of Operación Galgo; she was acquitted in 2011. In May 2013, it was reported that Domínguez had failed a bio-passport test in 2009. In 2015, she was banned from competing for three years by the Court of Arbitration for Sport for irregularities in her biological passport and stripped of her status as a Spanish national athlete. This annulled all of Domínguez's competitive results from August 2009 to July 2013, including her 2009 world championship in steeplechase. Her personal best in the steeplechase is now listed by the IAAF as 9:09.39 from the last race she ran six days before the official doping ban period went into place.

Domínguez competed early in her career at 1,500, 5,000 and 10,000 metres. She competed as a 20-year old in the 1996 Summer Olympics, finishing 9th in her initial heat in the 1,500m event. In 1998 Domínguez won her first championship medal in the European Championships in Budapest in the 5,000m, winning bronze behind Sonia O'Sullivan, who won gold and Gabriela Szabo, who took silver. In 2002, she won these events at the European indoor and outdoor championships, and won her second straight title in 2006 in the 5,000 metres at the European outdoor championship (also obtaining the Championship Record). She also has silver medals from the World Championships in 2001 and 2003, and she was named Spanish Athlete of the Year in both years.

Domínguez is a six-time national champion in the women's 5,000 metres. Her only Olympic appearance in the event was in 2000. She missed the 2004 Summer Olympics due to injury and returned in 2005 with a 14th place at the World Championships.

In 2006, after winning the gold medal at the European Championship in the 5,000 metres, she became the most decorated Spanish athlete ever. She also broke the Spanish record at the 10,000 metres at the same event, where she finished 7th. In addition to her track career she has competed in cross country running, winning the Cross de Atapuerca in 2006 and taking the title at the European Cross Country Championships the following year. She ended 2007 with a win at Palencia's most prominent international athletics competition, the Cross Internacional de Venta de Baños.

During the 2008 season, Domínguez started running the 3,000 metre steeplechase, breaking the Spanish record in her first race. Contesting the event at the 2008 Summer Olympics, Domínguez was among the leaders with 250 metres to go, when she clipped a barrier and fell to the track. She did not finish the race.

Domínguez beat her own 3,000 metre steeplechase national record by over five seconds at a track meet in Málaga in June 2009. Following her improvements, she downplayed talk of medals at the 2009 World Championships, stating that she was only focusing on improving her technique and that Olympic Champion Gulnara Samitova-Galkina was a strong favourite. She then went on to win the gold medal in the event.