Marcelo Alberto Bielsa Caldera (Spanish pronunciation: [marˈse̞lo̞ alˈβ̞e̞rto̞ ˈβ̞i̯e̞lsa ˈkalde̞ɾa], nicknamed Loco Bielsa, "Madman" Bielsa, born July 21, 1955) is an Argentine association football coach and former defender, born in Rosario, Santa Fe. He is considered one of the most innovative coaches in the modern era and is the current manager of the La Liga side Athletic Bilbao. He is seen as one of the main proponents of the game's recent renaissance of total football along with former Barcelona coach Pep Guardiola.

Bielsa has managed not only football clubs but also the national teams of Argentina and Chile. In the latter country he achieved cult status due to the improved results of the national team under his leadership. His personality and gestures have in Chile captured the attention of media and unleashed a series of minor controversies both in the area of sports and in politics.In 1980 shortly after retiring from playing in professional football, Bielsa decided to start a new career as a football manager. His first assignment was coaching the youth divisions of Argentine club Newell's Old Boys. In 1990 Bielsa was given the task of managing Newell's first team where he would later go on to win the 1990 Torneo Apertura and the 1990-91 Torneo Integración defeating Boca Juniors in penalties. El Loco managed the squad that competed in the final of the 1992 Copa Libertadores losing to São Paulo on penalties. Weeks later after enduring defeat in the Copa Libertadores final, Bielsa and Newell's won the 1992 Torneo Clausura.

Bielsa is a municipality located in the province of Huesca, Aragon, Spain. According to the 2004 census (INE), the municipality has a population of 463 inhabitants.

The Bielsa tunnel under the Pyrenean mountains connects Bielsa and Aragnouet in France. It was first opened in 1970. In 2002, the French government unilaterally decided to close the tunnel to heavy-goods vehicles over 3.5 tonnes, a decision which caused serious concern in Aragon.