Teachers' ability to elicit and use evidence of student thinking during instruction is critical in high-quality mathematics instruction. The practice of anticipating students' mathematics supports teachers in noticing and being prepared to respond to student thinking during in-the-moment instruction. To date, most research on anticipating has involved teachers in formal professional learning contexts such as university coursework or professional development programs and has focused on identifying and describing teachers' anticipations. However, few studies have investigated anticipating in the context of professional practice or how it is enacted by teachers with a variety of experiences. This study examines three secondary mathematics teachers' practice of anticipating students' mathematics. Using a multi-case study design, it examines the ways in which these three teachers anticipate, the resources they draw upon, the purposes they have for engaging in the practice and highlights similarities and differences in their enactments. Findings indicate that when anticipating the ways students will engage with cognitively demanding mathematics tasks, teachers first consider their instructional contexts, including their curricular programs, academic standards, and the focal mathematical ideas for units of instruction. To varying degrees, they develop records of mathematical activity students might demonstrate and conjectures about ways students might think mathematically when engaging with these tasks. Beyond these similarities, teachers in this study drew upon different domains of knowledge and enacted the practice for different purposes. Results of this study have implications for mathematics teacher educators working to support mathematics teachers learning to anticipate as well as researchers investigating instructional practices in context. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]