Ever since the phrase, 'the happy athlete' was introduced into the FEI rules for dressage (Article 401.1) there have been discussions about what this actually means and whether it is possible to recognize and reward positive emotions in working horses. For those interested in the study of equine behaviour, the use of such subjective terms for assessing horse emotion during training and performance, is interesting in that this suggests that horse trainers, riders and judges feel that there are meaningful behavioural expressions of emotional state that can be accurately assessed whilst the horse is at work and during competition. Although there has been much more research into the recognition of negative emotions such as pain, fear and stress in horses, recently there have been a number of studies attempting to look at what horses choose and how they may express pleasure or even happiness. 'Putting the welfare of the horse as a happy athlete at the heart of everything we do', is one of the main values quoted by equestrian bodies, however if we are to manage equine welfare we need to measure it and how successfully this can be done relies upon the development and validation of robust yet practical welfare indicators. Until recently, welfare assessment has traditionally focused on the absence of experiences that induce negative emotions. However, the notions of quality of life, a life worth living and the concept of the happy animal are starting to become more accepted within the animal welfare field with the assumption that if an animal is experiencing positive emotions, then its welfare needs can be said to be met, and if negative, then they are not and welfare is of concern. So the pertinent question is, what is welfare in the context of the horse used for equitation purposes? And what are the most useful welfare indicators for judging the emotional state of an individual horse within the context of the training and performance situation? In this review paper we will examine the results of recent work in this area, and the challenges such research poses both in relation to the science, but also to the use of horses for recreation and sport.