This symposium was organized to give four young psychologists, who were chosen as being interested in developmental researches out of eleven selected, the opportunity to report what they had gained from participating the 21st ICP. They had several times of disccusion beforehand and also had leading developmental psychologists in Japan answer a question-naire on methodological issues of their fields. Four interesting problems emerged from these processes, and each speaker reported his thoughts and impressions through the ICP on each topic as follows. ``Theory and Application'' (Nobuko Uchida) Hypotheses for constructing any developmental thory should be tested as naturally as possible. At the ICP, majority of individual papers were based on the laboratory work only, and the theme of symposia and lectures were mostly under the influence of Piaget's theory. ``Necessity for the Ecological Approach" (Nobumoto Tajima) The ecological stuy can be regarded as a source of hypotheses and variables in question. The hypotheses ought to be tested in laboratories and their varidity should again be verified in an ecological setting. Few ecological studies were presented at the ICP, with an exception of Witkin, H.A., who advocated the necessity for the eco-cultural approach in his field. ``Importance of the Longitudinal Study'' (Michiko Takahashi) Understanding of the importance of early experiences and the research movement from descriptive studies to scientific explanation underlie today's need for the new type of longitudinal study which is more than repetition of the same treatment at different age levels. Resbarcher's role as an intervener in the program should be regarded as one of the active and influencial factors. There was no presentation based on this new type of longitudinal study at the ICP. ``Cross-Cultural Study'' (Naomi Miyake) At international conferences, some have begun to emphasize the importance to guarantee the cross-cultural equivalance of psychological construct in question itself, rather than that of tools and analytic methods only- Cross-cultural studies would be useful for researchers to realize that there is always the cultural relativity in the human sciences. Their presentation was followed by the active discussion with participants from the floor and the speakers are heartily thankful for their seniors' sincere concern toward them. In addition to what they gained through the ICP, their experience at this symposium would surely motivate their further researches.