Fast field cycling (FFC) offers a unique window on molecular dynamics for in vivo applications, thanks to its ability to measure the NMR dispersion profile. This chapter summarises the different technologies that have been developed to exploit FFC-MRI for biomedical applications since the first attempts around 1990, using a range of technology that has been developed to investigate the rich source of information provided by T1 dispersion. The chapter also discusses how FFC technologies based on resistive coils present some important limitations, including in the design of pulse sequences or in the quality of the data. In addition to reviewing important technologies and methods from a number of techniques in various laboratories, including Overhauser imaging, pre-polarised MRI and delta relaxation-enhanced MRI, we present some of the new challenges that human-sample FFC brings to magnetic resonance imaging (MRI) through illustrations from the recently completed resistive 0.2 T FFC-MRI system developed in the University of Aberdeen FFC laboratory. Finally, this chapter presents some of the promising results from medical studies on cancer, muscle damage and osteoarthritis, illustrating the possibilities offered by FFC-MRI in the search for entirely new biomarkers that might be used to improve the diagnosis and monitoring of disease in the future.