The essential purpose of life-span developmental psychology is to describe and explicate the intra-individual continuity or change in human development. Yet, truly empirical studies are only emerging. In that sense, planning of this special issue was especially timely, and the three papers of high value, not only as an introduction of methodology to analyze developmental process and mechanism, but also as a guide to indicate possible future research designs and styles in developmental psychology. Although SEM is a very useful tool, without adequate review of theoretical issues, it could possibly churn out meaningless results. We need detailed theoretical investigation and hypothetical thinking before data collection and analysis, and have to check results against the reality and evaluate effect sizes in order to interpret findings correctly.