A central issue of human-animal interactions has been, and continues, to be mainly focused on the emotional and positive aspects that fixe the imagination of both public and researchers. It is particularly highlighted in the use of animals in therapeutic situations that involved ‘weaker’ people. After a historical report and a clarification of the term ‘animal assisted therapy’, we propose to develop a critical review of these particular therapies using horses as well as other species (i.e. dog, dolphin). It is firstly required to establish why animals are widely considered as potential therapists. We examine the theoretical framework included the relaxing effect and the social substitute status that animals can have, as well as the simple non verbal interactions between human and animal developed. We secondly describe several empirical researches to illustrate the heterogeneity (e.g. people, animal used) as well as the weakness of these studies (e.g. methodological devices, subjectivity, case studies) with a focused on autistic disorders. Thus, clear scientific evidence is still lacking and a need arises to better understand the relations between people and animals especially in a reproducible therapeutic ways. A project is currently led by different scientific teams to explore finely the relations between children, both with typical and autistic development- and animals, according to different contexts. We here present some results that reveal, on the one hand, the importance of owning a pet in the development of children with autism. On the other hand, the practice of horse riding is explored both in a typical practice in an equestrian club and in a therapeutic way. The results show an impact on children behaviors with unfamiliar animals. Other results are also discussed in the light of animal assisted therapies, providing us some ways of thinking about methodology and studies in research and the applications of animals in assisted therapies.