This volume summarises the outcome of the 13^th Workshop of the International Association of Phytoplankton Taxonomy and Ecology (IAP) on if, and if so under what conditions phytoplankton assemblages reach equilibrium in natural environments. Quite a number of ecological concepts use terms such as: ecological equilibrium, stability, steady-state, climax, stable state, etc. However, these ecological concepts often have been "translations" of scientific theories developed in physics or chemistry but they almost always lack scientific corroboration, the problem being that often these...