The barnacle Austrominius modestus, native of New Zealand and Australia was introduced to the South of England around 1943 and has since spread to most coastal waters in Western Europe, including the southern North Sea. Apart from an ephemeral incursion into the Danish Wadden Sea in 1978, since 2010 it has established permanent populations capable of reproduction along the North Sea coast of the Jutland peninsula, the Limfjord, the north-western Kattegat, and the Skagerrak. It has probably invaded Danish waters by pelagic larvae originating in the German Wadden Sea. The species has since spread to other Danish localities, likely following the prevailing currents, but other means, as for instance transport by vessels, are possible. The barnacle inhabits stones, stone-reefs, mollusk shells, and live shore crabs in shallow waters. Based on hydrographical data from its native and recently invaded areas, we predict its future distribution to extend to most coasts of continental Europe except for brackish waters (<20 PSU), and the Arctic seas. The northernmost distribution limit may include the Lofoten Islands of Norway.