A rich and diverse literature exists on the effects that human interviewers can have on different aspects of the survey data collection process. This research synthesis uses the Total Survey Error (TSE) framework to highlight important historical developments and advances in the study of interviewer effects on a variety of important survey process outcomes, including sample frame coverage, contact and recruitment of potential respondents, survey measurement, and data processing. Included in the scope of the synthesis is research literature that has focused on explaining variability among interviewers in these effects and the different types of variable errors that they can introduce, which can ultimately affect the efficiency of survey estimates. We first consider common tasks with which human interviewers are often charged and then use the TSE framework to organize and synthesize the literature discussing the variable errors that interviewers can introduce when attempting to execute each task. Based on our synthesis, we identify key gaps in knowledge and then use these gaps to motivate an organizing model for future research investigating explanations for interviewer effects on different aspects of the survey data collection process.