The rheology of xanthan solutions is strongly influenced by molecular association and aggregation. The relationship between rheological behavior and molecular association has been studied using dynamic oscillatory measurements, step‐shear‐rate measurements, and optical birefringence. For solutions with concentrations of 0.5% wt or below, weak association—possibly through hydrogen bonding—leads to nonlinear behavior in dynamic oscillatory measurements at high strain. For concentrations of 1% and above, liquid crystalline domains are formed and the time required to approach a steady viscosity value at low shear rates is quite long.