The number of adults living in households with only a cell phone has now reached approximately 10% of the total population, according to extrapolations from governent surveys. This phenomenon presents the potential for a serious non-coverage bias in RDD telephone surveys conducted only on landline phones. To estimate the impact of this bias, the Pew Research Center conducted four independent studies in 2006, including two with the Associated Press, that sampled from both the landline and cell phone RDD frames. Each of these studies included at least 200 interviews with cell-only respondents. Topics covered in the surveys included the following: attitudes about technology and use of technology and gadgets; basic social and political attitudes and values; media consumption habits; political participation and attitudes toward political engagement. AII four studies reached the same conclusion. Although cell-only respondents are different from landline respondents in important ways, they were neither numerous enough nor different enough on the key dependent variables to produce o significant change in the overall survey estimates when included with the landline samples and weighted according to U.S. Census parameters on basic demographic characteristics. The paper will describe the basic differences between the cell-only and landline respondents as well as the process and consequences of including cell-only respondents in the overall survey samples. The paper will also summarize describe the practical issues and cost implications of including cell-only respondents.