A Subway Series is a series of Major League Baseball games played between teams based in New York City.

The term's historic usage has been in reference to World Series games played between New York teams, but since 1997 it has also been applied to interleague play during the regular season between the American League New York Yankees and National League New York Mets. Play during the regular baseball season between the New York Giants and the Brooklyn Dodgers, both of the National League, from their origins in the 1880s until both left the city after 1957 was not called a Subway Series. The Yankees have appeared in all Subway Series games as they have been the only American League team in the city.

The all-New York match-ups in World Series play have to-date been the following:

• 1921 - New York Giants defeat New York Yankees, 5 games to 3.
• 1922 - New York Giants defeat New York Yankees, 4-0.
• 1923 - New York Yankees defeat New York Giants, 4-2.
• 1936 - New York Yankees defeat New York Giants, 4-2.
• 1937 - New York Yankees defeat New York Giants, 4-1.
• 1941 - New York Yankees defeat Brooklyn Dodgers, 4-1.
• 1947 - New York Yankees defeat Brooklyn Dodgers, 4-3.
• 1949 - New York Yankees defeat Brooklyn Dodgers, 4-1.
• 1951 - New York Yankees defeat New York Giants, 4-2.
• 1952 - New York Yankees defeat Brooklyn Dodgers, 4-3.
• 1953 - New York Yankees defeat Brooklyn Dodgers, 4-1.
• 1955 - Brooklyn Dodgers defeat New York Yankees, 4-3.
• 1956 - New York Yankees defeat Brooklyn Dodgers, 4-3.
• 2000 - New York Yankees defeat New York Mets, 4-1.

(Note: The 1921 World Series used a best-of-nine format.)

The first few of these World Series are generally not regarded as true "Subway Series". The 1921 and 1922 match-ups were in fact played in a single ballpark, as both the Giants and Yankees then played at the Polo Grounds in Manhattan. The venues for the 1923, 1936 and 1937 World Series, the Polo Grounds and Yankee Stadium in the Bronx, were a short walk apart across a bridge over the Harlem River.

Usage of the term "Subway Series" arose in 1941 when the Dodgers made their first World Series appearance since 1920. The subway had become an important form of public transport in the city and provided a convenient form of travel between Brooklyn's Ebbets Field and Yankee Stadium.

More recently, play between the Yankees and Mets at Yankee Stadium and Shea Stadium in Queens has sometimes been wittily referred to as the Triborough Bridge Series, as that bridge provides the fastest route between the two ballparks.

In addition to the five World Series played between the Yankees and Giants prior to 1940, the two teams also played exhibition series against each other from time to time. The match-ups were known as the "City Series" and were sometimes played in October while other teams played in the World Series.