The second city of a country is the city that is (or was) the second-most important, usually after the capital or first city.

Criteria for second city status include population size, economic or commercial importance, political importance, or some cultural sense. Since it is often difficult to draw a precise boundary where cities end, deciding which city is second in a country is not always straightforward. If the cultural definition is used, then the choice of second city is highly subjective and a matter of opinion rather than fact. In many countries, more than one city might have a legitimate claim to being second city, depending on the definition or criteria used.

It is also sometimes believed, rightly or wrongly, that the second city would assume the role of capital city (as seat of government, market trading, etc.) if the capital were to be compromised by invasion or insurrection.

Second city may also refer to the second largest by population size, ecomonic, commercial, political, or cultural importance in the context of the subnational entity, instead of the nation.

The Second City is a long-running improvisational comedy troupe based in Chicago's Old Town neighborhood.

The Second City Theatre opened on December 16, 1959 and has since expanded its presence to several other cities, including Toronto, metro-Detroit, Las Vegas, Los Angeles, and New York. The Second City has produced television programs in both the US and Canada including SCTV, Second City Presents, and Next Comedy Legend. Since its debut, Second City has consistently been a starting point for several comedians, award winning actors, directors, and others in show business.