Herein, we provide a detailed review, describing the clinical trials that led to the FDA approval of the BTK inhibitors for management of Chronic Lymphocytic Leukemia (CLL), Mantle Cell Lymphoma, Marginal Zone Lymphoma (MZL), Follicular Lymphoma (FL) and Waldenstrom Macroglobulinemia (WM). The gene discussed is BTK; the disease is marginal zone lymphoma.