<p>Bacteria have multiple mechanisms through which they sense changes in their environment and respond appropriately. In some instances, bacteria appear to retain an imprint of past events that can influence future behaviour, resembling a form of memory. This Perspective explores this concept of bacterial memory at the genetic, epigenetic, biochemical and ecological levels. We discuss how memory can prime bacteria to respond appropriately to recurring stimuli, providing fitness benefits in fluctuating environments. At the cellular level, there is evidence for memory storage mechanisms involving mutations, DNA methylation, or the inheritance of metabolites or proteins that provide a means of accessing past experiences. Complex bacterial communities can exhibit ecological memories of past environments, stored as microbiota population changes that persist or lag after acute environmental change. We review the emerging evidence supporting these concepts of microbial memory, outline some of the key molecular mechanisms, and identify research gaps and potential future applications.</p>