Resting respiratory sinus arrhythmia (RSA REST) indexes important aspects of individual differences in emotionality. In the present investigation, the authors address whether RSA REST is associated with tonic positive or negative emotionality, and whether RSA REST relates to phasic emotional responding to discrete positive emotion-eliciting stimuli. Across an 8-month, multiassessment study of first-year university students (n= 80), individual differences in RSA REST were associated with positive but not negative tonic emotionality, assessed at the level of personality traits, long-term moods, the disposition toward optimism, and baseline reports of current emotional states. RSA REST was not related to increased positive emotion, or stimulus-specific emotion, in response to compassion-, awe-, or pride-inducing stimuli. These findings suggest that resting RSA indexes aspects of a person’s tonic positive emotionality.