Solid dispersions and mixtures of quercetin and poly(vinylpYrrolidone) (PVP) K30 are studied by differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and heat capacity (C) measurements. The IUPAC name for PVP is 1-ethenylpyrrolidin-2-one, and that for quercetin is 2-(3,4-dihydroxypheny1)-3,5,7-trihydroxy-4H-1-benzopyran-4-one. A solid dispersion is found in the region of w(1) < 0.5, and a solid mixture is found in the region of w(1) > 0.5, where w(1) is the mass fraction of quercetin. The C data is correlated to temperature T by a polynomial equation, and changes in enthalpy and entropy were calculated from C(p). The C(p) data is valuable in the evaluation of drug efficiency.