The book introduces Tadeusz Kotarbiński’s philosophy of action into the mainstream of contemporary action-theoretical debates. Piotr Makowski shows that Kotarbiński–Alfred Tarski’s teacher and one of the most important philosophers of the renowned Lvov-Warsaw school—proposed a groundbreaking, original, and (in at least a few respects) still fresh perspective in action theorizing. The book examines and develops Kotarbiński’s ideas in the context of the most recent discussions in the philosophy of action. The main idea behind Kotarbiński’s action theory—and thus, behind this book—is the significance of the philosophical investigations of the general conditions of effectiveness, efficiency, and economy of intentional actions. Makowski presents and reinterprets Kotarbiński’s views on these dimensions of our activities and sheds new light on the most important areas of action theory.