Survey participants are increasingly responding to Web surveys on their smartphones as opposed to their personal computers (PCs), and this change brings with it some potential data-quality issues. This study reports on a randomized crossover experiment to compare the effect of two different devices, smartphones and PCs, on response quality in a Web survey conducted in a probability-based panel. Participants (n = 1,390) were invited to complete an online questionnaire on both a smartphone (mobile Web) and PC (PC Web) in sequence. We hypothesized that smartphone use would result in lower-quality responses because people are more likely to use smartphones while multitasking or while around other people and because they could have difficulty recording their answers using a small touchscreen. While we found that respondents who participated in this study were more likely to multitask and more likely to be around other people when using smartphones, these factors had little impact on data quality. Respondents were at least as likely to provide conscientious and thoughtful answers and to disclose sensitive information on smartphones as on PCs. When using smartphones, however, respondents seemed to have trouble accurately moving a small-sized slider handle and a date-picker wheel to the intended values. Overall, we find that people using smartphones can provide high-quality responses, even when their context is more distracting, as long as they are presented with question formats that are easy to use on small touchscreens.