 We focus almost exclusively on moral theories from the 20th century and later; the exception is Kant, with whom we begin. After briefly discussing Kant, we move on to the non-naturalist moral theories presented in the early part of the 20th century by Moore and Ross. We then consider naturalist moral theories developed much later in the 20th century, and close by considering particularism and more recent versions of intuitionism that are descendants of the positions developed by Moore and Ross.