Political trust is crucial for a well-functioning society. Yet few countries enjoy the benefits of high political trust. This makes people wonder how trust in institutions is built. While trust in political institutions is considered to be an individual's evaluation of institutional performance, individuals within the same country make very different assessments. In this dissertation, I show that personality traits, that are genetic and socialized at an early age, can help explain why individuals' trust assessments differ. As personality traits reflect individuals' behavioral, cognitive, and emotional patterns, I argue that traits affect political trust in three ways, directly through our general tendencies, indirectly through how we process information and experiences, or how we interact with institutions. In three research papers, I study the relationship between personality traits and political trust in different political contexts, using different measurements of personality traits, political institutions, and institutional experiences. The results show that personality traits contribute to explaining why individuals' levels of trust in the same institutions differ. I conclude that personality traits are an important explanation for how political trust is formed and need to be considered when studying how trust changes over time.