In museums and laboratories, collections constitute material reservoirs for knowledge and today history and science recombine in new ways to generate knowledge from collections. This special issue, Collections, Knowledge and Time, treats collections broadly across museums of history of medicine, history of science, natural history and ethnography, as well as scientific institutions including biobanks, seed banks and fly centres investigating how collections overlap and change status and use. We focus in particular on the temporal dynamics of collections: the layering and interweaving of asynchronous temporalities as collections are preserved, frozen, re-interpreted, sampled and deteriorated over time, and how these temporalities constitute knowledge potentials.