 Until quite recently it seemed that neutral monism (in its traditional form) was a brief and unimportant sideshow on the grand stage of metaphysics. Notwithstanding the fact that the three main protagonists—Mach, James, and Russell—were important figures, whose ideas profoundly influenced many areas of contemporary thought, their speculations about neutral monism seemed to have vanished from the philosophical scene. But the current wave of interest in the traditional versions of neutral monism, as well as the lively development of alternative versions of neutral monism, indicate that neutral monism may, once more, become a live option in the ongoing efforts to explore the metaphysics of mind.