The invasive oriental shrimp Palaemon macrodactylus Rathbun, 1902 has considerably extended its distribution in transitional waters along the Atlantic and Channel coasts of France during the period 2007-2010. The most probable method of a primary introduction of this species is ballast waters, but passive transport by water currents is also a possible mechanism of colonization (secondary introductions). Palaemon macrodactylus is a powerful invader of transitional waters and these new populations should be monitored in the future to assess any consequences to native species.