B lymphocytes are specialised leukocytes essential to the adaptive immune response, characterised by specificity and memory, in contrast to innate immunity. They mediate humoral immunity by targeting extracellular pathogens, while T lymphocytes are pivotal in intracellular antigen destruction and immune regulation. The differentiation of B cells begins with hematopoietic stem cells (HSCs), pluripotent cells in the bone marrow that generate all blood cell lineages. HSCs differentiate into myeloid and lymphoid lineages, giving rise to B and T lymphocytes. During development, B cells acquire antigen-specific receptors (B-cell receptor, BCR) and express CD20, a key surface antigen critical for their identification and therapeutic targeting. Monoclonal antibodies against CD20 are a cornerstone of multiple sclerosis treatment. They deplete B cells, modulate immune responses, and reduce disease activity. Anti-CD20 therapies, including ocrelizumab, ofatumumab, rituximab, and ublituximab, vary in binding site specificity, molecular structure, pharmacokinetics, and administration routes, impacting their efficacy and safety profiles. CD20 is also expressed in a rare subset of T cells with unique pro-inflammatory properties, highlighting its diverse immunological roles. This review explores the biology of CD20-positive lymphocytes, the mechanisms of action of anti-CD20 therapies, and their applications in multiple sclerosis. It discusses the nuances of efficacy, immunogenicity, and adverse effects, including neutropenia and secondary immune dysregulation, providing insights into personalised therapeutic strategies.