Currently, teachers increasingly use digital curriculum resources in the design and enactment of their lessons. Using digital resources changes how teachers interact with their resources and how students interact with teachers and content, placing new demands on teachers. This study examines this context. The research questions guiding this study were: 1) What factors influence how teachers use digital curriculum resources when designing middle school math units? 2) How do teachers use digital resources to facilitate lessons? Using qualitative methods, based in a reflective investigation methodology (Gueudet & Trouche, 2012a), I followed three middle school mathematics teachers' curriculum resource practices as they designed and enacted a unit of instruction, typically ten days. The teachers came from a district that recently underwent a digital conversion by providing teachers and students iPads and laptops to use for instruction. I frame teachers as designers and used multiple frameworks to examine their work with digital resources. More specifically, I used documentational genesis (Gueudet & Trouche, 2009) to examine teachers' creative processes, and the notion of learning spaces (Pepin et al., 2017) coupled with the replacing, amplifying, and transforming (RAT) framework (Hughes et al., 2006) to examine teachers' use of digital resources during instruction. My analysis of the interviews provided insights into factors influencing teachers' use of digital resources, whereas my analysis of the observations provided insights into how teachers incorporated digital resources into instruction. Findings align with the view of teaching as complex, context-dependent work where digital resource use is shaped by professional obligations. Prioritized obligations influence how teachers create teaching resources. Understanding resource systems provides a nuanced view of teaching and teachers' multiple design goals. Additionally, digital resources create new demands when orchestrating lessons. [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://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]