Theranostics is revolutionizing medical science by seamlessly combining diagnostics with targeted therapies to advance precision medicine. This integrated approach uses sophisticated tools like biological pathways, nanotechnology, and molecular engineering to accurately diagnose diseases and deliver personalized treatments. Traditional methods such as radiopharmaceuticals, biomarker analysis, and transarterial chemoembolization have provided the groundwork for aligning therapy with diagnostic insights. However, recent innovations, including nanotheranostics, artificial intelligence, and genomic technologies, have taken personalized medicine to new heights. These breakthroughs utilize nanoscale carriers, advanced imaging techniques, and cutting-edge therapies like CAR-T cells and liquid biopsies to improve effectiveness while reducing side effects. Additionally, artificial intelligence and next-generation sequencing enable clinicians to analyze complex data and forecast treatment responses, paving the way for a more precise and patient-focused approach to healthcare. This chapter delves into the journey of theranostics, examining the interplay between traditional practices and modern advancements and their combined role in addressing challenging diseases such as cancer.