Operant procedures occupy a prominent role within animal welfare science because they provide information about the strength of animals' preferences. It is assumed that strongly motivated choices commonly indicate conditions necessary for uncompromised welfare. A review of the literature shows that members of many species will work for access to resources not commonly provided to them; including a secure resting place (perches for hens or boxes for rodents) and substrates for species-typical activities such as nesting, digging and rooting (in hens, rats, mice and pigs). Despite a recent surge in popularity, operant techniques remain under-utilised and studies employing them struggle to find the best method for prioritising resources. In order to fully exploit the potential of operant procedures a wider appreciation of the relevant theories and techniques might be beneficial; including greater employment of the basic principles of reinforcement theory and further development of more complex economic analogies. If these two strands of research develop together, operant approaches have a key role to play in refining and replacing husbandry practices that undermine animal welfare.