Two crystal polymorphs of 1,7-bis-(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione (curcumin) have been obtained by crystallization from ethanol solution. The polymorphs have been characterized by DSC, IR spectroscopy and XRPD and shown to be the previously described forms I and III. The solubility of both polymorphs in ethanol and of one polymorph in ethyl acetate has been measured between 10°C and 50°C with a gravimetric method. Primary nucleation of curcumin from ethanol solution has been investigated in 520 constant temperature crystallization experiments in sealed, magnetically stirred vials under different conditions of supersaturation, temperature and agitation rate. By a thermodynamic analysis of the melting data and solubility of form I, the solid state activity is estimated from 10°C up to the melting point. The solubility is lower in ethanol than in ethyl acetate, and in both solvents a positive deviation from Raoult's law is observed. Form I has lower solubility than form III and is accordingly thermodynamically more stable over the investigated temperature interval. Extrapolation of solubility regression models indicates that there should be a lowtemperature enantiotropic transition point, below which form I will be metastable. By slurry conversion experiments it is established that this temperature is below -30°C. All nucleation experiments resulted in the stable form I. The induction time is observed to decrease with increasing agitation rate up to a certain point, and then increase with further increasing agitation rate; a trend previously observed for other compounds. By correlating the induction time data obtained at different supersaturation and temperature, the interfacial energy of form I in ethanol is estimated to be 3.0 mJ/m 2 .2