This review compiles, summarizes and provides new analytical insights on large amounts of fragmented information on the diets and feeding behaviours of syngnathids (Family Syngnathidae). This review is broken down into two distinct sections that address two central questions: (1) How, where, when and what do syngnathids eat? And (2) How does diet differ with feeding morphology? For (1) we summarized both qualitative and quantitative information on the diets and feeding behaviours of syngnathids found in the published and grey literature. This section includes a narrative summary of syngnathid feeding events and foraging behaviours (e.g. body mechanics and feeding morphologies, habitat use, seasonal and diurnal timing of feeding, energetics) and a tabulated summary of what syngnathids eat. For (2) we performed a comparative analysis on the diets of 41 species of syngnathid, comprising 15 genera from 39 sources in peer-reviewed and grey literature. Redundancy analyses on bulk, numeric, and frequency of occurrence data, analyzed separately, all show large unexplained dietary variation, which we hypothesize is the result of large differences in prey availability. Of the explained variation, syngnathid diets were most strongly correlated with head characteristics: most notably relative snout lengths and gape sizes. Syngnathid feeding morphologies also showed high phylogenetic signal; this suggests that dietary differences across genera were largely explained by how syngnathids differed with respect to these feeding morphologies. This review identifies new taxonomic patterns, and expands on previous generalities, improving our ecological understanding of this diverse group of fishes.