Philosophy's Margins draws together neglected texts from philosophy's archive to argue for close attention, within intellectual history, to how thought takes form. The book's particular focus is on an alternative intellectual history for philosophy's development in the first half of the twentieth century. It considers the lively philosophical imaginations and experimental forms of writing of five thinkers: Victoria Welby, Vernon Lee, May Sinclair, Alain Locke, and Susan Stebbing. The first three wrote from the margins of academic philosophy as it became an increasingly professionalised discipline, while the careers of the last two contour that shift. Their work suggests various ways in which philosophy's cultural, political, and personal vitality might be sustained against or alongside academic specialization. This book brings together archival research and a close reading approach to explore these writers' radical but under-studied contributions to philosophy's conceptual and cultural history, as well as to cultural modernism. In doing so, it aims to offer a new account of what philosophical writing has been and can be. Turning to notes in book margins, parables in private letters, verse translations, family diaries, a failed thesis, and other such unorthodox forms, it uncovers a lively transatlantic response to pragmatist philosophy, which became a litmus test for thinkers navigating questions of how to write about the world, words, and truth.