The authors investigated changes in self-efficacy in writing and writing apprehension in a sample of first-year college students in an interdisciplinary writing-intensive course taught by faculty from varied disciplines at a liberal arts college. Results showed that self-efficacy in writing significantly increased while writing apprehension decreased significantly from the beginning to the end of the semester. In addition, writing apprehension partially mediated the effect of self-efficacy in writing on performance, as measured by course grades. These findings highlight the importance of looking beyond students' ability and instructor course design to the role of self-efficacy and apprehension in understanding students' writing performance. (Contains 4 tables.)