Abstract: One methodological challenge developmental research has been facing is that the development of skills in different domains is subject to large individual variability. Assessing this variability requires the use of microgenetic research designs that measure development with high temporal frequency at the time when it occurs. In this talk, we present an integrative approach that combines a population-based prospective, longitudinal, and microgenetic research paradigm by means of a simple- to-use, smartphone-based developmental diary application (kleineWeltentdecker App; see http://www.weltentdeckerapp.ch). The WeltentdeckerApp targets parents of children between birth and 6 years of age. Parents are prompted periodically to answer a short set of questions about their children’s development in different domains (language, cognition, motor skills, and socio-emotional competences). These questions are extracted from a database of approximately 2000 questions (language incl. vocabulary, syntax, grammar: > 1500, motor (incl. fine and gross motor): 176, cognition: 34, social-emotional: 74) that have been validated per domain and for different age groups. In addition, physiological aspects such as height and weight and contextual aspects such as parental education, SES, languages exposure, and cultural background are assessed. The WeltentdeckerApp is available in German, French, Italian, and English. The assessment of children’s development is therefore far less limited to specific regions, countries, and languages than in traditional research approaches and allows longitudinal assessment of children at different ages, world-wide. Data will be presented from the validation studies and we will offer a first analysis of the data of currently > 1.600 parents who are using the WeltentdeckerApp with a current total number of > 60.000 data points. By means of this novel microgenetic approach, we expect to learn more about developmental processes and their dynamic interactions in children aged 0 to 6 years. Authors: