In April 2011, the U.S. Census Bureau conducted an Internet test of the American Community Survey (ACS), in which different mailing materials and mailing strategies were used to offer an Internet reporting option for the survey. In two conditions, an Internet reporting option was initially offered, with a paper form following in a subsequent mailing. Only the timing of the subsequent mailing varied in those conditions. In two other conditions, both modes were offered simultaneously, but the panels varied the amount of emphasis on the Internet option. In April and May, the Census Bureau fielded a follow-up telephone survey of approximately 1,700 ACS respondents and nonrespondents to the Internet Test survey. This follow-up study gathered information about how effectively the mailing materials for the Internet Test conveyed the response option choices. Questions in this follow-up study focused on which components of the mailing materials or mailing strategy motivated sample households to respond by the Internet or by the paper form. The follow-up also contained questions to determine why some households did not respond at all. This paper presents results from the follow-up telephone study of respondents and nonrespondents to the 2011 ACS Internet Test. Results of the follow-up study show that the majority of respondents knew they could respond either by paper or via the Internet to the ACS. The results did not provide substantial support for the finding in the literature (e.g., Millar and Dillman, 2011) that offering multiple modes simultaneously and forcing participants to make a reporting mode choice is the reason why some participants never respond. Instead, many nonrespondents in this study claimed never to have received the ACS envelope; if they did receive the envelope, many said they did not open it because they were too busy.