Computer-assisted personal interviewing (CAPI) offers many attractive benefits over paper-and-pencil interviewing. There is, however, mixed evidence on the impact of CAPI on interview length, an important survey outcome in the context of length limits imposed by survey budgets and concerns over respondent burden. In this article, recent experimental and quasi-experimental evidence derived from a large, nationally representative household panel study is used to investigate CAPI’s impact on interview length. We find that effects very much depend on how CAPI is implemented, including the hardware and software adopted, the extent and nature of dependent data, and even interviewer workloads—a finding that helps explain the conflicting results from previous studies. Overall, our study leads us to the conclusion that, absent dependent data, CAPI is likely to increase interview lengths, but the potential reductions from dependent data are very large, such that even modest levels can lead to net reductions in interview lengths.