Image-based biomarkers that report on specific cell phenotypes in the body are highly valued for disease detection and monitoring cytotherapies. Towards this need, there is sustained scientific interest in fluorine-19 ( F) magnetic resonance imaging (MRI) for molecular–cellular imaging applications. The attraction of F tracer MRI is its ability to produce pure ‘hot-spot’ images, an absence of false-positive signals, robust quantification, and tracer safety. For molecular–cellular applications, fluorine MRI does not require a pre-scan prior to tracer administration, thus offering several advantages over metal–ion-based proton ( H) contrast-agent approaches. Key applications of F MRI include cell tracking, inflammation detection, and biosensing. Fluorinated imaging tracers can also serve as therapeutic agents or drug-delivery vehicles. Over the past decade, the field of F MRI has seen remarkable innovation in tracer designs and detection methods as well as the realization of its clinical potential.