Introduction: The approach that observes the manifestation of personality in behavior through repeatedly measured personality states has been gaining increasing research attention. Personality states, measured multiple times, form a density distribution, and previous research has shown that there is a large amount of intra-individual variability in these states. However, although there is considerable variability in personality states, the distribution mean (i.e., aggregated state) is considerably correlated with the corresponding personality trait. Besides the relationship of aggregated states with corresponding personality traits, research has also examined predictors of intra-individual variability in personality states. The development of taxonomies of psychological characteristics of situations enabled researchers to examine situational determinants of variability in behavior. Another aspect related to intraindividual variability in personality states identified in previous research is momentary affect. Finally, the validity of average personality states compared to personality traits as a measure of personality was examined through a comparison of their nomological networks. The aim of this research was to examine the expression of basic personality traits through states, characteristics of situations and current affect as its possible predictors, as well as to compare the relationships of traits and average states of personality with their nomological network, i.e. the network of their correlates. Methodology: The first step of the research consisted of the construction of a measure of the state of personality and its validation in a pilot study, which was followed by the main study. A pilot study was conducted on a sample of psychology students from the Faculty of Croatian Studies, 106 of them. In the main research, a sample of participants consisted of the students from the Faculty of Humanities and Social Sciences, mostly psychology students, and 170 of them. Experience sampling was used as a method of data collection. Participants reported four times a day for eight days about their personality states, characteristics of situations, and current affect. Data were also collected on their personality traits, as well as a set of correlates. Results: Replicating results from the previous studies, it was found that there is a great amount of intra-individual variability in personality states. Average personality states were also highly correlated with the corresponding personality traits. Variability in personality states within individuals could be predicted to some extent based on perceived characteristics of the situation and current affect, thus indicating that there are both stable and variable determinants of personality expression in behavior. By comparing the relationship that the average states and corresponding personality traits have with the nomological network of correlates, it was found that they are very similar, but could not be treated as equivalent. Conclusion: The obtained results indicate that the expression of personality in behavior is determined not only by stable characteristics (i.e., personality traits), but also by variable characteristics, which, in the current research included psychological characteristics of situations and momentary affect. This finding contributes to a perspective that represents a reconciliation of dispositional and situational approaches to describing behavior. Finally, a comparison of nomological networks of aggregated personality states and their corresponding personality traits contributed to the evaluation of construct validity of aggregated personality states as a measure of personality.