Bioimaging in vivo and in vitro of cells and animals enables the scientific community to study physiological processes, toxicity of compounds, and mechanisms of cell death. All the insights gained from these studies enable the development of better therapeutics. Bioimaging agents range from emissive organic molecules, to polymers, to systems containing metals. In this chapter, we will highlight recent advancements in the development and use of metalcontaining systems, molecular, polymeric and nanostructures, for bioimaging of cancer cells and tumors in animals.