We are in the process of updating and extending the OPAL equation-of-state (EOS) and opacity data to include low-mass stars. The EOS part of that effort now is complete, and the results are described herein. The new data cover main-sequence stars having mass >=0.1 Msolar. As a result of the more extreme matter conditions encountered with low-mass stars, we have added new physics. The electrons are now treated as relativistic, and we have improved our treatment of molecules. We also consider the implications of the new results for helioseismology.