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Animals make frequent decisions about what food to eat, as well as how, when and where to obtain it, and must decide correctly on most occasions if they are to grow and reproduce. Observations of foraging animals. help document what they eat, but the processes underpinning food assimilation, the dietary choices of foragers and shaping the food webs in which they are embedded often remain obscure. To clarify animals' choices, especially under natural conditions, field experiments are often necessary. Here, I describe a range of experiments using examples from diverse animal taxa in aquatic and terrestrial environments, highlighting studies with robust sampling and experimental designs that allow strong inferences from the results. Experimental approaches furthering our understanding of feeding have used clay and plasticine models, odourbased models, lures and baits, sensory manipulations and memory-testing protocols. Conversely, approaches quantifying constraints on food acquisition have experimentally manipulated the magnitude of putative constraints, such as competition and predation, or manipulated foragers' perceptions of constraints, such as in giving-up density experiments. Other experimental approaches uncovered food preferences using cafeteria trials, where foragers have a choice of different food, and tethering experiments using live prey to measure predation rates. Other field experiments use food addition or withdrawal to quantify influences of food on individual forager fitness and the dynamics of consumer populations; carcass-addition experiments represent a modified food-addition design providing foragers with …