My main research interest is in general relativity and cosmology. I am particularly interested in the theory of the inflationary universe. Thanks to rapid progress in observational cosmology, we have begun to see the linear vacuum fluctuations from inflation, and we will be able to detect nonlinear, non-Gaussian fluctuations from inflation soon. However, our understanding of inflation is still very limited, and far from a quantitative level. What I am interested in now is looking for new observational signatures that can distinguish differences between different models, to identify the physics behind inflation, and to possibly find traces from physics beyond inflation. In this respect, in addition to electromagnetic waves as an observational tool, gravitational waves will certainly play a central role in cosmology, particularly in exploring early universe physics in coming years. I am currently working on gravitational wave cosmology with this expectation.