Knowledge of the thermal conductivity of a functional semiconductor is important for device design; for electronic applications, large thermal conductivities are desired to minimize Joule heating whereas small thermal conductivities are desired for thermoelectric applications. For many organic crystals, available samples are too small and/or fragile for conventional measurement techniques. We have developed “ac” techniques for measurements of anisotropic thermal diffusivities in materials ranging from single crystals of TIPS-pentacene to textured polymer (PEDOT) blends. Thermal conductivities are then determined by comparison with the specific heat, measured by differential scanning calorimetry. In these measurements, the front surface of the sample is heated with chopped light and temperature oscillations on the back surface are measured. “In-plane” thermal conductivities are measured by using low chopping frequencies and studying the spatial dependence of the oscillating temperature with a thermocouple glued to the surface when the front surface is partially blocked by a movable screen. For TIPS-pentacene and related materials, the in-plane thermal conductivity is comparable to organic metals such as TTF-TCNQ, materials with excellent intermolecular pi-orbital overlap. PEDOT blends can also exhibit relatively high thermal conductivities when the fibers are partially aligned. Transverse thermal conductivities are determined by measuring the dependence of the temperature oscillations on the chopping frequency. Because the thermocouple response time can be affected by the “glue” with which it is attached to the sample, for these measurements we determine the temperature oscillations by measurements of the oscillating infrared radiation from the back of the sample by mounting it in front of an MCT detector. For textured PEDOT blends, the transverse thermal conductivity is low, as expected. For TIPS-pentacene and related materials, however, the transverse thermal conductivities are an order of magnitude larger than the in-plane, and are in fact comparable to materials with extended bonding such as sapphire. This result suggests non-negligible dispersion of transversely polarized optical phonons, i.e. significant interactions between molecular oscillations, presumably librations, of side groups oriented between the layers.