Background. Dispositional optimism is a relatively stable tendency to expect positive outcomes in life. Given ample evidence that optimists lead happier and healthier lives than pessimists, the lack of research on the origins of individual differences in optimism is surprising. It has been proposed that parents likely play an important role, but empirical research is largely lacking. The aim of this study is to understand to what extent and how parents transmit optimism to their children. Methods. Ecological momentary assessments (EMA) are collected from 100 families to study the daily life dynamics between optimism, positive and negative affect, emotion regulation, and parenting behaviors in order to explain the intergenerational transmission of optimism. We expect that parental changes in optimism, positive affect and positive parenting have an effect on children and vice versa. Our approach enables an investigation of how these transactional processes between parents and children unfold in daily life. Main research questions are (1) At timepoints when parents experience higher levels of state optimism, (A) do they show more parental warmth and autonomy support toward their children? And (B) do their children experience a more positive day? (2) Is trait optimism in families associated with specific daily life moment-to-moment affect patterns, both within and between parents and children from the same family? Results. As data collection has not been completed, analyses have not been performed yet. Conclusion. During the presentation the focus will be on EMA data collection in families and how to analyze these data.