To improve tsunami disaster prevention, reliable prediction techniques for tsunami disasters are required. In this paper, the present techniques are reviewed and their directivities in tsunami research are discussed. Those techniques are divided into two periods. They are before and after a tsunami generation. In the former period, seismic information takes part in the prediction, and in the later period, tsunami information does. Offshore tsunami observation system, however, is not yet sufficient. The system which covers broad offshore region is expected.