Editorial to the first PECS 2004 special issue of Ocean Dynamics.

This article reflects on the 12th International Biennial Conference on Physics of Estuaries and Coastal Seas (PECS) held in Mérida, México from October 19 to 22, 2004. PECS philosophy has been to stimulate the cooperation between the coastal engineers and coastal oceanographers. The topic of PECS 2004 was Hydrodynamics and Morphodynamics in Estuaries and Coastal Seas, including estuarine hydrodynamics, coastal hydrodynamics, coastal transport and morphodynamics.