Dietary supplements, such as oral vitamins, minerals, and herbals cannot be marketed with claims to prevent or treat disease. Yet, they are typically recommended, used, and expected to improve a person’s health. Unlike prescription and over-the-counter medications, dietary supplements are not approved by the US Food and Drug Administration (FDA) for safety and efficacy. They are categorized by the FDA among many food products for which labeling about content and claims about purpose, safety, or efficacy are best regarded as marketing. This issue investigates why buyers and clinicians should not only beware of dietary supplements’ risks, but also carefully consider their beliefs about roles these underregulated products play in forming expectations, planning care, assessing risk, and sustaining a $35 billion US market.