Bruton's tyrosine kinase (BTK) is a part of the B-cell receptor (BCR) signaling pathway.Activation of the BCR appears crucial for normal B cells as it regulates proliferation, differentiation, adhesion, survival, and apoptosis. Such signaling is also vital for malignant B cells, since many of them show constitutive activation of the BCR pathway. The development of ibrutinib, a best-in-class BTK inhibitor, has led to a new direction in the treatment of B-cell malignancies. Further studies have enabled the development of more potent and more selective BTK inhibitors, such as zanubrutinib. These novel agents were designed primarily to reduce adverse effects such as diarrhea, atrial fibrillation, rash, or hemorrhagic complications.Compelling data from clinical studies that have verified its efficacy and safety has allowed the approval of zanubrutinib in hematological malignancies such as mantle cell lymphoma, Waldenström's macroglobulinemia, chronic lymphocytic leukemia, and marginal zone lymphoma.