STS describes how knowing practices work by including, drawing on, and reproducing heterogeneous material and immaterial infrastructures. Typically taken for granted, these infrastructures both shape knowing and are (re)crafted in those practices. This chapter uses four environmental projects (Scallops seeding in Saint Brieuc Bay, France; the designation of a marine protected area in Arran, Scotland; salmon management in Deatnu, Norway; and a civil laboratory in Newfoundland, Canada) to illustrate the political nature of the infrastructures of knowledge, and how these condition, but do not determine, what is possible.