This review discusses the rapid progress in understanding thermal transport in nanoscale devices and materials, emphasizing experimental, theoretical, and computational developments over the past decade. It highlights the importance of interfaces between materials, where thermal conductance has been studied experimentally but observed properties differ significantly from theoretical predictions. Classical molecular dynamics simulations are emerging as a powerful tool for calculating thermal conductance and phonon scattering, offering a promising interplay between experiment and theory. The review also addresses fundamental issues in defining temperature in nonequilibrium nanoscale systems and the challenges of thermal management in modern Si microelectronics, where the close proximity of interfaces and small heat dissipation volumes significantly affect thermal transport. Additionally, it explores the unique transport properties of low-dimensional nanostructures like carbon nanotubes and the impact of nanoscale porosity on thermal conductivity. The review concludes by discussing advances in measurement methods and the promise of improved thermoelectric materials, while acknowledging the ongoing challenges in understanding thermal transport in complex nanostructures.This review discusses the rapid progress in understanding thermal transport in nanoscale devices and materials, emphasizing experimental, theoretical, and computational developments over the past decade. It highlights the importance of interfaces between materials, where thermal conductance has been studied experimentally but observed properties differ significantly from theoretical predictions. Classical molecular dynamics simulations are emerging as a powerful tool for calculating thermal conductance and phonon scattering, offering a promising interplay between experiment and theory. The review also addresses fundamental issues in defining temperature in nonequilibrium nanoscale systems and the challenges of thermal management in modern Si microelectronics, where the close proximity of interfaces and small heat dissipation volumes significantly affect thermal transport. Additionally, it explores the unique transport properties of low-dimensional nanostructures like carbon nanotubes and the impact of nanoscale porosity on thermal conductivity. The review concludes by discussing advances in measurement methods and the promise of improved thermoelectric materials, while acknowledging the ongoing challenges in understanding thermal transport in complex nanostructures.