Due to low costs, speed, simplicity, interviewer assistance, and easy monitoring telephone interviewing had been the preferred mode of many survey practitioners for decades. However, technological developments related to information society, in particular the increasing rate of mobile-only individuals and households, are rapidly changing the survey research environment. In the first part of the chapter methodological issues of data collection by phone are delineated. After a brief history of phone surveys recent telephone use trends and their implications on survey coverage and sampling are outlined. Next, nonresponse in phone surveys is discussed. The section ends with an illustration of challenges posed by incorporating mobile phone in survey research. In the second part, phone surveys are discussed in the context of mixed modes, in particular their potential to improve coverage and response rates. Furthermore, data quality and cost issues are treated. Finally, the section introduces dual frame sampling of fixed and mobile numbers, a special type of mixed mode surveys that was developed to resolve the phone coverage problem. In the third part, the chapter deals with the optimization of telephone surveys according to costs and errors. An analytical solution for dual frame surveys and a more general postsurvey evaluation of different modes are presented. In conclusion, we recapitulate key issues of phone surveys and indicate future trends with guidelines for further research.