This book is an edited collection of essays in celebration of the centenary of Samuel Alexander's Space, Time and Deity, published in 1920. Samuel Alexander (1859-1938) was a leading figure of British philosophy in the early twentieth century. He was partly responsible for the 'new realism' movement along with G.E. Moore and Bertrand Russell. However, his work has been overlooked in developments of twentieth century philosophy and yet his theories and style of theorising are in vogue. This book begins with three previously unpublished papers by Alexander that shed light on his metaphysical commitments about time, universals, God, knowledge of past truths, grounding, and inference in logic and science. There are also two important posthumous chapters by philosophers of the mid-twentieth century, who elaborate on his life and most significant contributions. The second half of the book contains new essays by current scholars, discussing Alexander on metaphysical realism, idealism, naturalism, space and time, process ontology, ontological categories, epistemology, perception, philosophy of history, emergentism, and empiricism.