We have determined the apparent molar volumes V-phi and the apparent molar heat capacities C-p,C-phi for aqueous solutions of caffeine at temperatures T from 278.15 K to 393.15K, at the pressure 0.35MPa, and at molalities m from 0.01 mol . kg(-1) to 0.1 mol . kg(-1). We used a vibrating tube densimeter (DMA 512P, Anton PAAR, Austria) to determine the densities and volumetric properties, and a twin fixed-cell, power-compensation, differential-output, temperature-scanning calorimeter (NanoDSC 6100, Calorimetry Sciences, American Fork, UT, USA) to obtain the heat capacities. We have assumed that aqueous caffeine is described by a monomer-dimer equilibrium, and we have applied Young's Rule to fit our results with regression functions that are thermodynamically self-consistent and that include the equilibrium constant and the changes in enthalpy Delta(r)H(m), heat capacity Delta(r)C(p,m), volume Delta(r)S(m) and entropy Delta(r)S(m) for the monomer-dimer reaction over the ranges of temperature and molality of our experiments.