Self-regulation (i.e., the ability to regulate emotions, thoughts, and behaviors) develops rapidly during early childhood and promotes a broad range of developmental outcomes, such as academic achievement and social competence (Blair & Raver, 2015; Moffitt et al., 2011). Insight into factors that contribute to the development of self-regulation is therefore of crucial importance for early prevention of developmental problems. Neuroimaging research has revealed that the development of self-regulation is associated with activity of the frontal cortex, where frontal alpha and theta rhythms have been most commonly related to self-regulatory skills in young children (for reviews, see Klimesch, 1999; Marshall et al., 2002). For instance, higher frontal alpha power values have been related to better executive functioning (Broomell et al., 2020), whereas lower frontal theta power values have been related to better attentional ability (Perone & Gartstein, 2019). Maturational changes in these alpha and theta power values are assumed to be critical developmental markers (Clarke et al., 2001; Marshall et al., 2002). In general, it is assumed that brain maturation in young children consists of an increase in the amount of intermediate frequency activity (e.g., the alpha rhythm) and a decrease in the amount of lower frequency activity (e.g., the theta rhythm) from infancy through early childhood (for a review, see Cuevas & Bell, 2022). However, to date, the majority of developmental research focusses on maturational changes in EEG power in children above 3 years of age (Anderson & Perone, 2018; Cellier et al., 2021), a time when children typically develop higher order self-regulatory skills (Carlson, 2005). It might be the case that maturational changes in frontal EEG activity during infancy contribute to the emergence of higher order top-down mechanisms of children’s self-regulation, such as the ability to inhibit or delay behavior in accordance with task demands (for a meta-analysis, see Hofstee et al., 2022). Indeed, the first study that examined the relationship between frontal EEG maturation from 10 months to 4 years of age and children’s inhibitory control at age 4 revealed that, although initial levels of resting-state frontal alpha power were not associated with subsequent inhibitory control, greater increases in frontal alpha power across the study period were associated with better inhibitory control (Whedon et al., 2020). These results underline the importance of investigating whether maturational growth of frontal EEG activity during infancy and early childhood contributes to individual differences in child self-regulation. Yet, as the study of Whedon et al. (2020) exclusively focuses on EEG power in the alpha band, to our knowledge, it is currently unknown how maturation of frontal theta power across infancy and early childhood is related to the development of children’s higher order cognitive self-regulatory skills. In addition, previous research revealed gender differences related to frontal alpha and theta activity. Greater maturational changes in EEG power have been reported for girls, such as higher levels of alpha power at 4 years of age (Cuevas et al., 2016). Importantly, girls also show higher levels of self-regulation, such as better abilities to control inappropriate responses and behaviors (for a meta-analysis, see Else-Quest et al., 2006). This might be a result of greater brain maturation in girls than boys. However, to date, gender differences have not been sufficiently investigated in relation to brain maturation from infancy to early childhood. Thus, the current study aims to examine (1) the maturational changes of frontal EEG alpha and theta activity from infancy into early childhood, (2) the relation of the initial levels and the maturational changes of frontal EEG alpha and theta activity with children’s self-regulatory abilities, (3) gender differences in both maturational changes in frontal EEG alpha and theta activity and child self-regulation. Given that different measures of self-regulation might be differently related to frontal EEG activity (for a meta-analysis, see Hofstee et al., 2022), self-regulation will be assessed by both a parent-reported questionnaire and a behavioral task.