The present study developed and validated a 15-item self-report measure for boredom beliefs, the Boredom Beliefs Scale (BBS). We generated a pool of items on people’s lay beliefs about boredom from a series of qualitative interviews, and then administered it via an online questionnaire in Hong Kong Chinese (N = 231) and American (N = 498) samples. We identified 3 lay boredom beliefs—the extent to which people recognize the functions of boredom (boredom functionality), affectively dislike this emotion (boredom dislike) and normalize its experience (boredom normalcy). The 3-factor BBS was found to be measurement invariant across a two-week time interval and across the two cultural groups. Three subscales showed good internal consistency, test-retest reliability, and meaningful relationships with emotion beliefs, emotion acceptance, and boredom proneness. Implications of the scale in clinical and educational contexts were discussed.