Functional measures of nailfold capillaries (permeability, red blood cell velocity and oxygenation) offer value in disentangling the relationship between microvascular function and morphology. They offer the potential to further elucidate early disease changes that may occur prior to the vasculopathy observed in capillary architectural changes. In addition, they may be useful as sensitive outcome measures in clinical trials, to monitor response to (mainly pharmacological) treatment. These techniques currently remain in the research domain, due to their relative complexity and a slower rate of technological development than structural nailfold capillaroscopy; they still require validation. In this chapter we explore their current status, progress and limitations. We evaluate their potential in translation towards clinical application.