Cancer, a complex and heterogeneous group of diseases, continues to be a significant global health concern. Early detection, accurate diagnosis, and effective treatment improve patient outcomes. Biomarkers, encompassing a diverse range of molecules and genetic signatures, have emerged as indispensable tools in the fight against cancer. This chapter explores the multifaceted landscape of cancer biomarkers, delving into their types, discovery methods, established biomarkers in cancer, and clinical applications. Biomarkers in cancer are broadly categorized into genetic, proteomic, and metabolic markers, each offering unique insights into the disease. While established biomarkers such as BRCA1 and HER2 have paved the way for targeted therapies, ongoing research reveals a wealth of novel candidates. High-throughput technologies, including genomics, transcriptomics, and proteomics, play a pivotal role in biomarker discovery, aiding in identifying potential diagnostic, prognostic, and predictive markers. Clinical applications of cancer biomarkers are diverse, ranging from early cancer detection to monitoring treatment response and disease recurrence. Liquid biopsy is a noninvasive approach gaining prominence in capturing tumor-derived genetic material circulating in bodily fluids. While cancer biomarkers hold immense promise, challenges persist, including the need for rigorous validation, standardization, and addressing issues related to tumor heterogeneity. Nevertheless, they represent an invaluable resource in pursuing precision medicine and developing tailored treatment strategies, ultimately striving to improve the prognosis and quality of life for cancer patients. This chapter highlights the types of biomarkers, biomarker discovery methods, established biomarkers in cancer with case studies, novel and emerging biomarkers, clinical applications of cancer biomarkers, and challenges in biomarker development, including future perspectives.