The Pasig River (called Ilog Pasig in Filipino) is a river in the Philippines that connects Laguna de Bay to Manila Bay. Stretching for 25 kilometres (15.5 mi), it is lined by Metro Manila on each side. Its major tributaries are the Marikina River and San Juan River.

The Pasig River is technically a tidal estuary, as the flow direction depends upon the water-level difference between Manila Bay and Laguna de Bay. During the dry season, the water level in Laguna de Bay is low and the flow direction of the Pasig River depends on the tides. During the wet season, when the water level of Laguna de Bay is high, flow is normally from Laguna de Bay towards Manila Bay.

The Pasig River used to be an important transport route in Spanish Manila. Due to negligence and industrial development, the river has become very polluted and is considered dead (unable to sustain life) by ecologists. The Pasig River Rehabilitation Commission (PRRC) was established to oversee rehabilitation efforts for the river. Supporting the PRRC are private sector organizations, i.e. Clean and Green Foundation, Inc. that implemented the Piso para sa Pasig (Filipino: A peso for the Pasig) campaign.

The City of Pasig (Filipino: Lungsod ng Pasig) is one of the city-municipalities of Metro Manila in the Philippines and was the former capital of the province of Rizal prior to the formation of this grouping of cities designated as the National Capital Region. Located along the eastern border of Metro Manila, Pasig is bordered on the west by Quezon City and Mandaluyong City; to the north by Marikina City; to the south by Makati City, Pateros, and Taguig City; and to the east by Antipolo City, the municipality of Cainta and Taytay in the province of Rizal.

Pasig is primarily residential and industrial but has been becoming increasingly commercial in recent years. The old provincial capitol lies off of Shaw Boulevard, outside the city. Pasig is one of the three municipalities appointed by the diocese of the Roman Catholic Church in the Philippines (as the Roman Catholic Diocese of Pasig), making the Pasig Cathedral (formerly The Immaculate Conception Cathedral) the landmark coincide to its township in 1573.