Survey interviews are conducted to produce objective, accurate information in which interviewers ask questions as worded and their discretionary speech is carefully managed. To limit interviewer influence over answers and reduce between-interviewer variance, Standardized Interviewing (SI) requires interviewers to administer "nondirective probes" -- scripted utterances designed to elicit acceptable answers without leading respondents. To promote the intended interpretation of questions, and thus response accuracy, Conversational Interviewing (CI) authorizes interviewers to clarify questions when they suspect respondents have misunderstood. This article reviews evidence from 12 studies about the effectiveness of these two approaches. Findings consistently show that CI leads to considerably more accurate question interpretation and response accuracy than SI across different samples, modes, and languages, and does not increase interviewer variance. CI generally leads to longer interviews than SI, requiring practitioners to weigh increased response accuracy against longer interview duration. Several online implementations of CI have produced initially promising results.