Book excerpt: What kinds of curriculum materials do mathematics teachers select and use, and how? This question is complex, in a period of deep evolutions of teaching resources, with the proficiency of online resources in particular. How do teachers learn from these materials, and in which ways do they ‘tailor’ them for their use and pupil learning? Teachers collect resources, select, transform, share, implement, and revise them. Drawing from the French term « ingénierie documentaire »,we call these processes « documentation ». The literal English translation is « to work with documents », but the meaning it carries is richer. Documentation refers to the complex and interactive ways that teachers work with resources; in-class and out-of-class, individually, but also collectively.