The Japan Islands are located in a plate boundary where the Pacific, the Philippine Sea, the North America, and the Amurian plates converge one another. As a result of complex interaction among these plates, active deformation occurs throughout the region, causing many disastrous earthquakes. Therefore, monitoring of crustal deformation is of great importance. In Japan, the nationwide continuous GNSS network called GEONET was constructed in the middle 1990’s by the Geographical Survey Institute (currently the Geospatial Information Authority of Japan). With GEONET, crustal deformation of the Japan Islands has been continuously monitored and investigated in detail. Various deformation signals have been recorded in association with large earthquakes, interseismic coupling, slow earthquakes, volcanic activities, and so on. I will introduce representative observational examples of GEONET and discuss what we have learned from GNSS observation about crustal deformation during the last quarter-century.