Abstract The history of imaging dates back to 1895, with the invention of X-rays in 1895 by Conrad Rontgen and was first used to visualize a tumor by Franz Konig. In the 20th and 21st centuries, the field of imaging has been developing rapidly. Ultrasonography was another fundamental step in oncology imaging. This was followed by computed tomography (CT) scanning and continued by magnetic resonance approaches. Recently, more functional methods have been developed, such as positron emission tomography (PET) and hybrid techniques: PET/CT, PET/magnetic resonance imaging (MRI), and whole-body diffusion-weighted imaging. With the aid of imaging biomarkers, these techniques can be enhanced for visualizing cancer at earlier stages. Future directions in this field may focus on the adopting of both anatomical, molecular, and functional techniques and developing target-specific biomarkers. Within the progress of imaging techniques, living organisms can be visualized, characterized, and quantificated in cellular and molecular levels. Imaging systems can be classified according to the energy source used for obtaining visual information (X-rays, positrons, photons, or sound waves); the spatial resolution that is utilized (macroscopic, mesoscopic or microscopic); or the type of information that is attained (anatomical, physiological, cellular or molecular). In this chapter, anatomical and functional approaches will be firstly described. The prevalently used macroscopic imaging systems in preclinical and clinical applications—CT, MRI and ultrasound—and recently emerging molecular imaging systems—PET, single-photon emission CT, and hybrid technologies—will be described. Novel technologies such as bioluminescence imaging, near-infrared fluorescence, and photoacoustic imaging will also be explained.