Why does an object or phenomenon become the subject of scientific inquiry? Why do some of these objects remain provocative, while others fade from centre stage? And why do objects sometimes return as the focus of research long after they were once abandoned? Addressing such questions, this book is about how whole domains of phenomena - dreams, atoms, monsters, culture, society, mortality, centers of gravity, value, cytoplasmic particles, the self and tuberculosis - come into being and sometimes pass away as objects of scientific study. With examples drawn from both the natural and social sciences, and ranging from the 16th to the 20th centuries, this book explores the ways in which scientific objects are both real and historical. Whether discovered or invented, these objects of inquiry broaden and deepen in meaning - growing more 'real' - as they become entangled in webs of cultural significance, material practices and theoretical derivations. Thus their biographies should matter to anyone concerned with the formation of scientific knowledge.