The International Solvay Institutes deeply mourn the passing of Marie-Claude (“Mimi”) Solvay, whose steadfast support for fundamental research in physics and chemistry spanned more than six decades. We will forever cherish her generosity, her abiding faith in science and scientists, her thoughtful encouragement, and the warm hospitality she extended in her home to honor the participants of the Solvay Councils. A true grande dame has left us.