The Second Northern War (1655–1660, also First or Little Northern War, according to traditional Anglo-Saxon, German, Russian and Scandinavian historiography) is a name sometimes used for the series of conflicts between Sweden and its adversaries Polish-Lithuanian Commonwealth (The Deluge, 1655–1660), Russia (1656–1661), Brandenburg-Prussia (1657–1660), the Holy Roman Empire (1657–60) and Denmark-Norway (1657–1658, 1658–1660).

The same wars are sometimes referred differently in other countries: for example in Poland The Deluge sometimes is a name for the series of wars against Sweden, Brandenburg, Russia, Transylvania and Cossacks.

In these conflicts England is consistently an ally of Sweden whereas the Dutch Republic often intervenes against the Swedes.