The thermal conductance of interfaces is a key factor in controlling thermal conduction in nanostructured materials, composites, and individual nanostructures. We have recently advanced the state-of-the-art of time-domain-thermoreflectance (TDTR) measurements of thermal transport and are using TDTR to study heat transport across individual interfaces with extremely high and low thermal conductance; and heat transport in nanoscale multilayers that circumvent the lower-limits for homogeneous materials imposed by the minimum thermal conductivity. The 3 μm spatial resolution of our TDTR measurements also enables rapid high-resolution imaging of the thermal conductivity of complex microstructures and combinatorial samples. Heat transport in suspension of carbon nanotubes and metal nanoparticles are studied by picosecond transient absorption. Most of the vibrational modes of a carbon nanotube are weakly coupled to their environment; by contrast, the thermal coupling of metal nanoparticles to surrounding water is surprisingly efficient.