Monocytes are amoeboid-shaped, mononuclear leukocytes that differentiate from the monoblast precursor in the bone marrow. They then circulate in the blood, making up between 3% to 8% of the population before settling into various tissues and further differentiating as resident macrophages or dendritic cells. CD14 and CD16 are defining cellular marker for monocytes, and subtypes are defined depending on their level of expression. Monocyte isolation products are convenient tools for the further investigation of these immune cells.