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. Documentation refers to the complex and interactive ways that teachers work with resources, in-class and out-of-class, individually, but also collectively.