Marginalia is a term used to describe written notes or verbal comments spontaneously offered by participants over the course of a study. Although typically ignored, this unexpected form of data offers psychologists an opportunity to listen when participants “speak back” to the researcher. In this introduction to this special section on marginalia in Qualitative Psychology, I argue for recognizing marginalia as data. In addition, I discuss relevant research on marginalia in the social sciences and describe evidence for how marginalia offer an invaluable tool for researchers to examine their own assumptions about research design and data collection. The authors included in this special section describe their experiences with analyzing marginalia in studies using survey, interview, and participatory research methods. Each article discusses challenges the authors faced when thinking about marginalia. This involved shifting from thinking about marginalia as “noise” to thinking about marginalia as an important source of data. This special section on marginalia offers strategies that extend calls from feminist writers of color to recognize the margins as locations of political knowledge, a challenge to status quo assumptions, and critical spaces for knowledge production.