This supplement of Mikrochimica Acta contains selected papers from the Fourth Workshop of the European Microanalysis Society (EMAS) on "Modern Develop- ments and Applications in Microbeam Analysis" which took place in May 1995 in Saint Malo (France). EMAS was founded in 1986 by members from almost all european countries in order to stimulate research, applications and development of all forms of microbeam methods. One important EMAS activity is the organisation of biennial workshops for demonstrating the current status and developing trends of microanalytical techniques. For this meeting, EMAS chose to highlight the following topics: Monte-Carlo simula- tions, transport calculations and use of soft X-rays for electron probe microanalysis (EPMA), dynamic secondary ion mass spectrometry (SIMS), detection of small quan- tities using different techniques: synchrotron radiation X-ray fluorescence, particle in- duced X-ray emission (PIXE), cathodoluminescence microscopy (CL). Two new kinds of instrumental techniques were also presented: atomic probe and scanning probe microscopy (STM). The aim of the conference is to give introductory lectures corresponding to the topics of the meeting and to have contributions in the form of po- ster sessions. More than 80 posters were presented. Most of them gave a short oral pre- sentation. The poster subjects were related to the use of microanalytical techniques: EPMA with wavelength dispersive spectrometry (WDS) and energy dispersive spec- trometry (EDS), Auger electron spectrometry (AES), secondary ion mass spectro- metry (SIMS), scanning electron microscopy and other topographical methods like scanning tunneling microscopy (STM) or atomic force microscopy (AFM).