Purpose: Decades of scholarship have drawn on Weiss's four categories of research use (Weiss, 1980; 2005; Weiss & Bucuvalas, 1980) -- instrumental use, symbolic use, conceptual use, and imposed use -- to examine how research use unfolds in school districts (e.g., Amara et al., 2004; Penuel et al., 2017). In this paper, we theorize a new form of research use: latent use. We do so by drawing on sociocultural learning theory (Wenger, 1998) and using empirical data from our comparative case study of research use across four districts. We define latent use as when educators participate with research-embedded tools in ways that guide their work practice. Latent use occurs both when educators describe themselves as using research but also when they do not explicitly acknowledge their use of research. Research Design: We surveyed 12-15 district leaders from the thirty largest district offices. We then purposively sampled four districts -- districts with high and low connections to outside sources of research, and districts that possessed greater and fewer routines. These districts serve from approximately 70,000 to 180,000 students, with over 50% of students eligible for free or reduced lunch. Over 18 months, we conducted a comparative case study on these districts' research use in literacy professional development (PD), collecting 140 interviews, 50 hours of observations, and 127 artifacts. For data analysis, coded and analyzed all references to tools in interviews and observations. We also coded for references to research embedded in all 127 tools. Finally, we conceptualized latent use by writing longitudinal memos of how district leaders used these research-embedded tools in all four districts. Findings: Latent use was pervasive across all four districts. Here, we draw on sociocultural theory (Wenger et al., 1998) to illustrate an example of latent use. In Juniper District, district leaders provided feedback on literacy PD using a research-embedded slide deck in Figure A. Uva says: so, let's do a whip around, and get the positives... Sharon says: I liked that the deck came back to the standards. Danika adds: I liked that it connected between reading and writing, with the standards. That's an important shift. Teagan adds: I want to second what Danika said on the reciprocal nature of reading and writing. I did a session last week with teachers, and that's something that they're missing. As illustrated in this excerpt, latent use has four defining characteristics. The first defining characteristic is that it involves tools that are not research products (e.g., journal articles) but nonetheless have research embedded in them (e.g., research citations), such as slide decks. Figure A is an example of a research-embedded tool. The second defining characteristic is that latent use requires district leaders to participate with a research-embedded tool. Through this participation, district leaders can make this tool meaningful in the context of their own work. We see this when Teagan made connections between the content of the slide deck on the reciprocal connections between reading and writing and her own experiences providing PD. The third defining characteristic is that latent use requires a research-embedded tool to guide how district leaders do their work. Here, the research-embedded slide deck, and specifically, Fordham and colleagues' research (see Figure A), focused and framed district leaders' discussions around literacy PD. The fourth defining characteristic is that latent use can occur regardless of whether district leaders acknowledge themselves as using research or not. When Danika and Teagan noted the "reciprocal nature of reading and writing," they were referencing Fordham's research idea without explicitly acknowledging its research base. Now that we have conceptualized latent use, we now detail how it differs from Weiss's existing categories of research use. Instrumental use. Instrumental use is when educators draw on research to fill a gap in knowledge when making a decision. During instrumental use, educators must intentionally seek out research to fill a specific gap in their knowledge. In contrast, educators who engage in latent use may not see themselves as using research. Additionally, whereas instrumental use informs formal decisions, latent use can guide a wider range of work practices. Symbolic use. Symbolic use is defined as the use of research to influence or persuade others about a decision or legitimize a decision that has already been made. When educators engage in symbolic use, they use research to justify what they were already doing, where research does not shift educators' work practices. In contrast, latent use involves educators using the research-embedded tools in ways that do inform their work practice. Imposed use. Imposed use is defined as when educators are required to use research when selecting an intervention curriculum or practice so they can receive federal or state funding. In contrast, latent use is not required by any entity. Conceptual use. Conceptual use is defined as the use of research ideas to inform how district leaders think about a problem or a solution to that problem. Whereas conceptual use involves changes to district leaders' thinking, latent use involves changes to leaders' work practices. Conclusion: Our discovery of latent use highlights a new pathway -- educators' use of research-embedded tools -- through which research informs practice. What was especially striking about latent use is that district leaders who engaged with latent use did not necessarily see it as a form of research use. For this reason, latent use may be hidden from view from both those engaging in latent use and researchers studying research use. Without attention to latent use, existing scholarship may be under-representing how frequently educators use research. Latent use raises important questions for embedding equity in research. Consider when the research embedded in tools is implicit or invisible (Cain & Allen, 2017). When educators do not see the full range of ways that they are using research during latent use, what are the implications for how they participate with research and who (and who does not) gets to meaningfully shape research agendas?