The 2023 Census Survey was the planned second iteration of the Small-Scale Response Testing (SmaRT) program that is part of the Census Bureau’s Small-Scale Testing Initiative. In preparation for the 2023 Census Survey, the Center for Behavioral Science Methods (CBSM) at the Census Bureau carried out cognitive testing of the mail materials intended to be sent to respondents who would participate in the survey. Nineteen participants provided feedback during the pretesting, and because the mail materials are bilingual in English and Spanish, testing was conducted in English and Spanish. The research questions included identifying any major comprehension issues with any of the mail materials, investigating how participants responded to the use of plain language, and testing the use of text message reminders to respond to the survey. In this paper, we present our findings and recommendations based on respondent feedback and spontaneous reactions, as well as observational and behavioral data.