Earthquake prediction is a field marked by uncertainty, as many of its fundamental questions remain unresolved. The situation is further complicated by the fact that earthquake prediction is closely tied to public policy and the assessment and management of risk. To better grasp the challenges in this field, I will examine the controversy around a prediction method proposed by a group of Greek scientists in the early 1980s. This controversy can be analyzed through the prism of the sound science–junk science debate, as scientists disagreed both over the feasibility and over the practical utility of different types of earthquake prediction. I will trace how the debate unfolded over the course of two decades, arguing that it could not be settled solely on factual grounds. Instead, I will highlight the role of values—and in particular, the values of precision and informativeness—in shaping the positions of opposing scientists and in influencing how earthquake prediction itself was defined.