In recent decades, an increasing interest in the dynamics of collections has brought to view how objects circulate as parts of networks of knowledge and how collections can acquire new meanings. Introducing this special issue on Collections, Knowledge, and Time, we want to shift focus from geographical circulation towards the temporal dynamics of collections: the layering and interweaving of asynchronous temporalities as collections are preserved, frozen, reinterpreted, sampled, and destroyed over time, and how these temporalities constitute knowledge potentials. We treat collections broadly across museums of history of medicine, history of science, and ethnography, and scientific institutions including biobanks, seed banks, and fly centres, to investigate the considerable overlap in collection practices, as well as how objects can move between cultural historical and scientific uses. We limit ourselves, however, to epistemic collections, mainly scientific ones, assembled with research as a main purpose. This introduction first explores apparently mundane collection practices such as preservation and care, as well as technologies such as freezers and boxes, to unravel them as temporal practices that make stored items transcendtime. We then discuss historical practices across cultural and scientific collections to show how historical thinking plays a central part in scientific collection work and how new scientific methods shape investigations of the past. Finally, we outline the potentialities for future knowledge in collections. In conclusion, we sketch out a pluralist epistemology of collections focusing specifically on how the dynamics of time create multiple epistemic potentials for historical scholarship and scientific research in the present and future.