This chapter provides a comprehensive overview of thermophysical properties and heat transfer phenomena at the micro- and nanoscale, which form the fundamental basis for Raman thermometry and related thermal characterization techniques. Section 1.1 introduces the background of thermal design and microscale heat transfer, emphasizing the deviation of heat conduction behavior from classical Fourier’s law as the characteristic length approaches the phonon mean free path. Section 1.2 discusses the physics of thermal transport in bulk and nanoscale materials, highlighting phonon scattering, boundary effects, and size-dependent thermal conductivity. Section 1.3 reviews electro-thermal characterization methods, including the 3ω method, transient electrothermal (TET), and thermoreflectance techniques, used to probe thermal conductivity. Section 1.4 focuses on opto-thermal methods, as a non-contact and high-spatial-resolution approach for temperature measurement.