Siero is a municipality of the autonomous community of Asturias, in northern Spain.

Siero's two main rivers, which run throughout much of the municipality, are the Nora and Noreña.

The area now known as Siero has been inhabited by humans since the Paleolithic period, especially near the current parishes of Argüelles, Lugones, and Samartindianes.

Following Enrique II's ascent to the throne of Castile, he exempted Siero from taxes due to its inhabitants' support during the Castilian Civil War.

In modern times, the tertiary sector has become Siero's largest, with construction and dairy farming still remaining relevant.