We conclude our extensive exploration of the cellular and molecular biology of the immune response by emphasizing studies that unveil the dynamic choreography of immune cells within living tissues. These images and videos have not only validated predictions made by immunologists who previously lacked the tools to visualize the cells they studied but have also uncovered unexpected characteristics of immune cells: the striking swarming behavior of neutrophils, the intricate dendritic processes of germinal center B cells, the coordinated interactions of B- T-cell pairs at the follicular boundary, and the distinctive appearance and activity of resident memory T cells in barrier tissues, to name just a few. The chapter concludes with an introduction to studies examining immune cell behavior in pathological conditions, which will serve as the foundation for the next series of chapters focusing on the dual role of immune cells in both combating and contributing to disease.