The germinal center (GC) is a microanatomical structure that nucleates from B-cell follicles in secondary lymphoid organs upon encounter of a foreign antigen. Within the GC, antigen-specific B cells undergo iterative cycles of somatic hypermutation, clonal expansion, and antigen-driven selection, favoring the output of long-lived plasma cells and memory B cells expressing high-affinity antibodies. These processes rely on spatially-confined interactions between GC B cells and immune and stromal cells, including follicular dendritic cells (FDCs) and T follicular helper (Tfh) cells, delivering survival and differentiation signals to ensure the positive selection of GC B cells expressing the highest-affinity B cell receptors (BCRs).