Monocytes are a type of large white blood cell that circulates in the bloodstream and differentiates into macrophages or dendritic cells upon entering tissues, playing a crucial role in innate immunity and inflammation. They are essential for phagocytosing pathogens, presenting antigens to lymphocytes, and orchestrating immune responses. Elevated monocyte counts can indicate chronic infections, inflammatory conditions, or haematological disorders such as monocytic leukaemia.