First-year principals encounter multiple messages about what it means to be instructional leaders; this may matter for how they enact instructional leadership. This cross-case qualitative study uses a qualitative approach of social network analysis to uncover the mechanisms through which first-year principals encountered particular beliefs about instructional leadership. To do so, I studied six first-year principals who came to their positions through four distinct paths, examining their informal social networks. I found, first, that their networks' structures influenced the spread of instructional leadership ideas from the environment to individuals at the mesolevel. Second, the findings suggest that preparation programs mattered for how the principals conceptualized instructional leadership. This research contributes to our understanding of the relationship between institutional ideas and practice in schools, principal preparation, and professional development. It also extends research on social network analysis by elucidating beliefs in the content of interaction in social networks.