The causes of the main states of suffering experienced by poultry species, namely fear, frustration and pain, are listed and the behavioural symptoms are described. Birds can be frightened by stimuli that are (1) sudden and intense, (2) novel, and (3) signalling special evolutionary dangers. The lack of a nesting site and lack of a roosting site in battery cages are the main causes of intense frustration in laying hens. Pain can be caused by feather pecking and cannibalism, the artificial environment, surgical procedures, and breeding practices. Possible solutions to these problems are suggested. Some other states of suffering including extreme hunger, behavioural restrictions not causing obvious frustration, and suffering due to social friction are also described. Possible solutions to all these welfare problems include changing the birds genetically, redesigning the birds’ environments and modifying husbandry procedures are discussed.