This study examined the perspectives of what high-quality mathematics instruction looks like. Written responses from preservice (n = 20) and inservice (n = 16) mathematics teachers were collected and categorized according to the Ten Principles developed by Anthony & Walshaw (2009). The responses of preservice teachers more often than inservice teachers included the categories of Building on Student Thinking and Mathematical Communication, while the responses of inservice teachers more often than preservice teachers included the categories of Arrangements for Learning and Making Connections. Both preservice and inservice teachers least often included the category of Mathematical Language in their responses.