A great progress was made in the study of geodesy and geodynamics by the adv ancement of space geodetic techniques. Each technique, however, has intrinsi c strength and weakness. Hence, the combination of different techniques is mutually beneficial. Prob lems in each technique will be clearly understood through the combination. I n particular, the different observation systems locating in a same area are most effective to see the systematic errors. Inconsistency which may be inv isible by a single technique are to be studied through the collocation. Meth odology of conventional surveying at a site is as important as the space geo detic measurements. Difference in the time variation is also an important to pic to be studied. As is seen in the Key Stone Program in Tokyo, we have sev eral stations in the world which were designed for collocation study. It is expected to improve the global reference frame by the collocation. Conventi onally the systems are collocated on the Earth. But the benefit of collocati on on the satellite or on the Moon are being discussed. Current status of c ollocation and combination of space techniques are reviewed.