Mary Baker Eddy (1821-1910) is best known for founding the religion of Christian Science - an international institution which has extended beyond her lifetime and into the twenty-first century. Often labelled as fringe theology, rather than core philosophy, Eddy's work has remained on the peripheries of academia. Her unmitigated idealism, and occasionally nebulous style, have led to a reluctance to apply a philosophical rigour to her thinking. In The Philosophical Foundations of Christian Science, Nicholas Sheldon rediscovers her as a radical philosopher, one of many female philosophers of her time who, he contends, should no longer be underestimated. Carefully analysing her non-linear style in order to understand her internal system of thought, Sheldon resolves flaws within her argument, and draws out Christian Science's remarkable philosophical assertion: that it is not only illness and suffering which are unreal, but the entire physical realm. For Eddy, it is only the spiritual which remains.