This paper summarizes and evaluates ecological long-term observations at the island of Helgoland (German Bight, North Sea). It is an introduction to a series of seven contributions to an issue of Helgoland Marine Research (vol. 58, no. 4) dealing with observations on the physico-chemical environment and the local biota (pelagic bacteria, phytoplankton, zooplankton, macroalgae, macrozoobenthos). More than 150 years of research at Helgoland (at the Biologische Anstalt Helgoland, BAH, since 1892), and particularly the Helgoland Roads time-series which started in 1962, has provided a multitude of data which represents a valuable basis for analysing past changes, evaluating the present status and predicting future changes in ecosystem parameters. Predicting the consequences of the recent rapid ecological change on regional and global scales requires increased efforts of focus on long-term ecological observations. Future efforts in this field will rely on the application of innovative advanced technology and on the concerted activities of a large number of institutions which only collectively can establish the large-scale patterns of temporal and spatial change in ecosystem functions. © Springer-Verlag and AWI 2004.