While mainstream psychology has made significant advances into the understanding of personality, applied linguistics research has offered a more muted response (Dörnyei and Ryan 2015) despite Bandura (2001:10) declaring that self-efficacy beliefs represent 'the foundation of human agency'. The study documented within this article therefore examines the contribution of personality traits from the five-factor model of personality to L1 (Japanese) and L2 (English) communication self-efficacy beliefs within a population of 300 Japanese university students. Through self-assessments drawn in relation to a hypothetical L1 and L2 interview encounter, and following a two-step process of hierarchical regression, the article shows to what extent personality traits make differentiated contributions to L1 and L2 communication self-efficacy beliefs.