For the past few years, molecular imaging and targeted drug delivery have been playing an important role toward personalized medicine. In designing and fabricating of multifunctional nanoparticles, the combination of imaging and therapeutic capabilities has also increasingly become important. As a result, a relatively new class of chemical compounds comprising dendritic polymers has been developed. This chapter highlights the potential of dendritic polymers in the growing field of theranostics. A controlled architecture with a high density of functional groups at the nanoscale size makes dendrimers optimal candidates for therapeutic approaches as well as in diagnosis. General aspects of chemistry and properties of dendritic polymers are described in the first section. Then, the biological scenario faced by dendritic polymers in biomedical application is discussed. An overview of selected therapeutic as well as diagnostic applications leads to the description of examples of recently developed theranostics.