g4view is a scientific application that permits to read geometry files at the Geant4 GDML format describing particle physics detectors. g4view permits to visualize the geometry of a loaded detector. It can read also "scenarios" files that permit to choose the volumes seen from GDML and strongly customize their graphical attributes as the coloring or the wire frame/solid rendering. A scenario permits also to customize an adapted particle source. From the main menu, you can then start a "particle through matter" simulation of the detector which is done by using the Geant4 toolkit. g4view can also read and execute "mac" files containing Geant4 scripting commands. Under the examples menu, there are predefined typical setups, as a piece of an electromagnetic calorimeter, intended to be used for particle physics detector teaching. We recall that Geant4 is a particle through matter simulation toolkit heavily used in high energy physics (for example at the CERN LHC experiments), but also for spatial and medical science. The web pages of g4view are under the "softinex" portal http://softinex.lal.in2p3.fr