Clark Ashton Smith (1893–1961) is best known for creating exotic worlds of fantasy, such as the lost continent Zothique, set in the far future, the arctic realm of Hyperborea, and the medieval domain of Averoigne. It is less widely known that Smith was a pioneer in science fiction, as his tales appeared extensively in such pulp magazines as Wonder Stories and Amazing Stories and had a marked influence on the science fiction of his day. Mars was a favored locale for several significant tales, including the cosmic horror masterpiece “The Vaults of Yoh-Vombis. ” “Seedling of Mars” is one of several tales in this volume that broaches the distinctive subgenre of “green horror”—horror that results from deadly animated plants. This motif first found expression in Smith’s early prose poem “The Flower-Devil,” and he utilized it in such tales as “Vulthoom,” “The Demon of the Flower,” and others. The remote planet Xiccarph is the setting for two tales, “The Maze of the Enchanter” and “The Flower-Women. ” One of Smith’s most expansive tales, “The Monster of the Prophecy,” is set on Antares, while the late story “Phoenix” is grimly apocalyptic in its setting in the far future, with most of the Earth’s inhabitants killed off. Clark Ashton Smith’s mastery of a prose-poetic idiom lends a distinctive flavor to his interplanetary tales. Far from being naively optimistic adventures into the depths of space, they exhibit a rueful doubt as to the place of human beings in an immense and hostile universe. This volume, edited by leading Clark Ashton Smith scholar Ronald S. Hilger, contains an illuminating preface by Nathan Ballingrud.