The Head of the Charles Regatta, also known as HOCR, is a rowing head race held on the penultimate complete weekend of October each year on the Charles River, which separates Boston and Cambridge, Massachusetts United States. It is the largest 3-day regatta in the world, with 11,000 athletes rowing in over 1,900 boats in 61 events. According to the Greater Boston Convention & Visitors Bureau, the three-day event brings 225,000 people to the Greater Boston area and $72 million to the local economy.

Rowing, sometimes called crew in the United States, is the sport of racing boats using oars. It differs from paddling sports in that rowing oars are attached to the boat using oarlocks, while paddles are not connected to the boat. Rowing is divided into two disciplines: sculling and sweep rowing. In sculling, each rower holds two oars, one in each hand, while in sweep rowing each rower holds one oar with both hands. There are several boat classes in which athletes may compete, ranging from single sculls, occupied by one person, to shells with eight rowers and a coxswain, called eights. There are a wide variety of course types and formats of racing, but most elite and championship level racing is conducted on calm water courses 2 kilometres (1.2 mi) long with several lanes marked using buoys.