The 1966 New York Giants season was the 42nd season for the club in the National Football League. The Giants finished in last place in the Eastern Conference with a 1–12–1 record, the worst in franchise history.
The 1966 Giants were the worst defensive team, in terms of points allowed, in the team's history. They allowed 501 points in 14 games, or an average of 35.8 points per game. This total broke the league record for the most points given up in a season. The next most points allowed by a Giants team was 427 in the 2009 season, which was 16 games. The Giants allowed opponents to score more than 30 points in eight of the 14 games, and gave up over 50 points three times.
On November 27, the Giants played the highest-scoring game in NFL history, losing to the Washington Redskins, 72–41. It was the first of three straight games in which the Giants gave up more than 40 points; they allowed 49 points against the Cleveland Browns and 47 versus the Pittsburgh Steelers.
With the addition of the expansion Atlanta Falcons, the NFL had 15 teams, necessitating the use of bye weeks. The Giants were the team that received the most centrally located bye, in Week 8, thus perfectly dividing their season into two 7-game halves. They failed to take advantage of this, however, losing all seven games after the break. (In contrast, the expansion Falcons were 0–8 before they got their bye in Week 9, but 3–3 afterwards.)