A new structural class of macromolecules, the dendritic polymers are nanometer sized, polymeric systems of hyperbranched materials having compact hydrodynamic volumes in solution and high, surface, functional group content. They may be water-soluble but, because of their compact dimensions, they do not have the usual rheological thickening properties that many polymers have in solution. Dendrimers, the most regular members of the class, are synthesized by step-wise convergent or divergent methods to give distinct stages or generations. Dendrimers are defined by their three components: a central core, an interior dendritic structure (the branches), and an exterior surface (the end groups). Over 50 compositionally different families of these nanoscale macromolecules, with over 200 end-group modifications, have been reported. They are characterized by nearly spherical structures, nanometer sizes, large numbers of reactive endgroup functionalities, shielded interior voids, and low systemic toxicity. This unique combination of properties makes them ideal candidates for nanotechnology applications in both biological and materials sciences. Dendrimers are core-shell nanostructures with precise architecture and low polydispersity, which are synthesized in a generation-by-generation fashion around a core unit, resulting in a high level of control over size, branching points, and surface functionality. The ability to tailor dendrimer properties to the needs of a guest molecule makes them ideal carriers for molecular encapsulation, allowing dissolution of hydrophobic materials in water and mixing of hydrophilic and hydrophobic compounds, for example in catalytic applications. Dendrimers are just one class of nano-sized materials that are explored to develop new life-saving technologies. Single-wall carbon nanotubes are used to make miniaturized sensors for DNA, pathogens, and chemicals – for example glucose sensors. Multi-wall nanotubes, nanoclays, and ceramic nanoparticles are incorporated in ultra-strong polymer nanocomposites that will be used in orthopedic, for example joint-replacement, applications. Nanoparticles can also be used to make nano-textured substrates to support attachment and growth of cells for tissue engineering.