Recent research on teacher professional development (PD) underscores the importance of the coherence of PD with standards, curriculum, and assessment. Teachers' judgments of the coherence of PD with larger system goals influence their decisions about what ideas and resources they appropriate from PD. Little research, however, has examined how teachers formulate these judgments and why teachers' judgments vary within the same system and for the same reform. In this article, we use organizational theory's concept of "sensemaking" to examine teachers' responses to PD related to the "Next Generation Science Standards" within two schools in the United States. Our study shows that teachers' perceptions of coherence emerge from interactions within PD, associated curriculum materials, and with colleagues and leaders in their schools. Some teachers, we found, were able to manage ambiguity, uncertainty, and perceived incoherence productively, while others foreclosed deep and sustained sensemaking. Our findings suggest the need for PD to engage teachers in sustained sensemaking activity around issues of perceived incoherence to bolster teachers' emergent understandings of standards and improve the likelihood of implementing instructional practices aligned to standards.