Scientific realism about spin is easily motivated. But what does it amount to? To answer this question, Chapter 3 contrasts in general terms two epistemological conceptions of realism—truth-content vs. progress realism—before problematizing truth-content realism in the context of quantum physics. After articulating the challenge faced by truth-content realism, the chapter argues that progress realism avoids it, offering a stable middle ground between anti-realism and traditional truth-content realism.