This chapter aims at understanding the issues of capturing vulnerable populations in large-scale quantitative surveys. A dilemma in survey construction arises when a target vulnerable population to be analyzed cannot be reached using standard survey designs. Indeed, adapting standard procedures may improve access to the targeted vulnerable population; however, these changes may lead to inaccurate comparisons with other population samples. To address this issue, this chapter deals with the data collection process of the large-scale survey on aging Vivre/Leben/Vivere: Old Age Democratization? Progress and Inequalities in Switzerland (VLV). It highlights the need to adjust standard procedures of a quantitative survey to access elderly migrants and the impact of doing so. Results show the need for a constant dialogue between the scientific requirements and realities of fieldwork to avoid an under-representation in surveys. Finally, providing resources to assess vulnerability is not only a methodological engagement; this is also a major social issue about giving a voice to the voiceless.