Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase involved in regulating cell proliferation, survival, and differentiation, with particularly important roles in neural development. Aberrant activation of ALK through gene fusions, mutations, or overexpression is a key driver in several cancers, including anaplastic large cell lymphoma and non–small cell lung cancer. Because ALK-driven tumors depend on this signaling for growth, ALK has become a major target in drug discovery. Studying ALK enables the development and optimization of selective kinase inhibitors, supports resistance-mechanism research, and has directly led to multiple successful targeted therapies, making ALK a textbook example of precision oncology in modern drug development.