When metal nanoparticles are excited by light resonant with the particle’s surface plasmon, non-radiative relaxation efficiently generates heat in the immediate region surrounding the particle. Such photothermal heating has been extensively explored in solution environments for applications such as cancer treatment and drug delivery. In contrast, use of and understanding of photothermal heating in solids, such as nanoparticle-polymer composites, has been limited. However, such photothermal effects could facilitate in situ thermal processing of polymeric materials via externally-controllable light excitation. The spatial specificity and temperatures achieved can potentially be used for triggering phase transitions, cross-linking, or driving region-specific chemical reactions inside the existing material. Anisotropic particles enable further tuning of the plasmonic frequency and polarization-controlled heating. By embedding fluorophores in the composite, a sensitive relative fluorescence approach can be utilized to dynamically monitor the average temperature within the sample as it is thermally processed. With modest light intensities and dilute nanoparticle concentrations, controllable temperature changes of several hundred degrees Celsius have been achieved.