Cancer represents one of the most complex and challenging health burdens of our time, affecting millions of individuals globally and spanning virtually every tissue and organ system in the human body. At its core, cancer is fundamentally a disease of cellular dysregulation where normal checks and balances on cell growth, division, and death become compromised, leading to uncontrolled proliferation and, in many cases, metastatic spread. This chapter explores the foundational principles underlying cancer biology, setting the stage for understanding current therapeutic approaches and future innovations in cancer treatment and prevention.