Cancer diagnosis is a rapidly evolving field with the integration of advanced molecular techniques in tumor diagnosis. Traditional diagnostic methods such as histopathology have been complemented by molecular tools that detect genetic, epigenetic, and proteomic changes associated with cancer. These molecular techniques include polymerase chain reaction (PCR), next-generation sequencing (NGS), fluorescence in situ hybridization (FISH), and liquid biopsy, among others. PCR allows for the amplification of specific genetic mutations or alterations, enabling precise detection of cancer-related biomarkers. NGS provides comprehensive insights into the genetic landscape of tumors, identifying mutations, copy number variations, and gene fusions, essential for targeted therapy selection. FISH and other cytogenetic techniques detect chromosomal abnormalities, such as translocations and amplifications, offering additional diagnostic and prognostic information. Liquid biopsy, a minimally invasive method, detects circulating tumor DNA (ctDNA), providing real-time insights into tumor evolution and treatment response without the need for invasive tissue biopsies. The clinical utility of these molecular techniques is vast as they have revolutionized the field of tumor diagnostics. They play a crucial role in early cancer detection, risk assessment, prognostication, and monitoring of treatment response or resistance. Additionally, they guide personalized treatment plans, allowing oncologists to select targeted therapies based on specific genetic mutations. Furthermore, molecular diagnostics are integral to the development of novel therapies, including immunotherapies and gene therapies. In this chapter, we aim to give an overview of current molecular techniques employed in cancer diagnostics and the clinical utility of these assays and how it impacts cancer patient management.