The article examines the relationships between personality traits and identity formation modes in both a theoretical and empirical manner. The sample consisted of 813 participants aged 18-65. The results indicate that personality metatraits Alpha and Beta can serve as core underpinnings of differentiation in identity formation, and that the relationships between these two personality metatraits and identity formation modes take a sinusoidal form, which is consistent with the circular organization of the Circumplex of Identity Formation Modes. The indicator of General Factor of Personality was the strongest connected to the circumplex dimension reflecting identity stability. At the Big Five traits level, two personality traits, Conscientiousness and Openness to Experience, were most strongly related to identity formation, while Emotional Stability predicted modes strongly but in a non-sinusoidal way. Thus, Conscientiousness and Openness to Experience can be seen as two basic underpinnings of identity formation, just as Agreeableness and Extraversion are responsible for interpersonal behavior in the Wiggins model.