Training immune cells to remember: Classical immunological memory, carried out by T and B lymphocytes, ensures that we feel the ill effects of many pathogens only once. Netea et al. review how cells of the innate immune system, which lack the antigen specificity, clonality, and longevity of T cell and B cells, have some capacity to remember, too. Termed “trained immunity,” the property allows macrophages, monocytes, and natural killer cells to show enhanced responsiveness when they reencounter pathogens. Epigenetic changes largely drive trained immunity, which is shorter lived and less specific than classical memory but probably still gives us a leg up during many infections. Science , this issue p. 10.1126/science.aaf1098

These guidelines are a consensus work of a considerable number of members of the immunology and flow cytometry community. They provide the theory and key practical aspects of flow cytometry enabling immunologists to avoid the common errors that often undermine immunological data. Notably, there are comprehensive sections of all major immune cell types with helpful Tables detailing phenotypes in murine and human cells. The latest flow cytometry techniques and applications are also described, featuring examples of the data that can be generated and, importantly, how the data can be analysed. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid, all written and peer‐reviewed by leading experts in the field, making this an essential research companion.