A boronic acid moiety can bind to nucleophilic species, such as fluoride ions and 1,2-diols, and arylboronates are converted to the corresponding phenols by treatment with hydrogen peroxide. Based on these reactivity profiles of boron compounds, a variety of boronic acid and boronate-based fluorescent chemosensors have been developed for detecting biologically relevant species. This feature article highlights recent advances that have been made in the development of chemosensors of these types for monitoring carbohydrates, dopamine, fluorides, metal ions and hydrogen peroxide.