During the past decade the space geodetic technologies have become a standard tool for monitoring of crustal deformations associated with volcanism. Since early 1990’s the GPS continuous measurement at 1,200 sites distributed throughout Japan have provided relevant information to understand ongoing magmatic processes beneath active volcanoes. During the crises of 1998 Iwate, 2000 Usu, 2000 Miyake and 2004 Asama, the GPS data played an important role to know magma migration sequence related to those volcanic activities. Synthetic Aperture Radar Interferometry (InSAR) also demonstrated its usefulness in volcanological applications. This technology enables us to map deformation field over a large spatial area without installing ground based observational instruments. During the 1998 Iwate crisis InSAR data acquired by JERS-1 satellite radar (functional during 1992-1998) provided key information about the deformations overlooked by other geodetic measurements. The developments of those space geodetic technologies are continual and further improvements will be achievable in terms of accuracy, rapidness of processing and completeness of temporal and spatial coverage. The geodetic data set will continue to be one of the major sources of information to understand volcanism in the forthcoming future.