The aim of this book is to explore the debate between Bas van Fraassen''s constructive empiricism and scientific realism. For this purpose I discuss the existence of observable and unobservable entities, the observation/theoretical dichotomy, inference to the best explanation, the no miracles argument, pessimistic induction, and epistemic risk. I strive to show that, contrary to the view of constructive empiricism, there is no clear demarcation line between observable and unobservable entities, and that not only naked eye observation but also the instrument-based observation plays an important role in acquiring knowledge. I agree with scientific realists that there is no highest point to the human power of observation; it is open-ended for further development. Moreover, naked eye observations are not themselves beyond doubt, as sometimes even naked eye observations deceive us. In that context, theoretical explanations help us to understand the real situation. As such, there is no reason to give more credit to naked eye observations than to instrument-mediated, theory-informed observations.