Cancer is one of the significant health problems in many countries worldwide and is the second leading cause of overall mortality. Early identification of cancer and proper monitoring are two essential aspects that influence cancer treatment success. However, both of these factors are influenced by the limitations of conventional techniques to diagnosis and therapy. Theranostics has garnered widespread attention from the scientific community due to its unique combination of therapeutic and diagnostic capabilities. The term “theranostics” is a combination of the words therapeutics and diagnostics. It can be diagnostic followed by therapy to stratify patients who are likely to respond to a specific treatment. In response to new developments in materials science and nanobiotechnology, scientists have used the unique electrical, magnetic, and optical properties of different types of nanocarriers for theranostic applications. Cancer theranostics is anticipated to be made possible by nanotechnology. The term nanotheranostics refers to specially designed nanometric drug delivery systems/nanoformulations that include nanocarriers/nanoparticles for theranostic applications. The present chapter discusses the theranostic application of different types of nontherapeutic in cancer treatment.