Science defines a chimera as an organism that consists of genetically distinct cell populations originating from different zygotes, which can descent from same or different species. Lack of research in the field of intraspecies chimerism raises the probability that chimerism is much more common in our environment. This fact is supported by diagnosis of chimerism in research done on animals, most often pets, who exhibited uncharacteristic coat phenotype whose cause still remains unknown. Chimerism in its lesser degrees, more known as microchimerism, presents transitory state in human as well as animal organisms worldwide. Any person who has transfused blood of transplanted organ becomes a chimera. This phenomenon can also be found in pregnant females whose placenta allows the entry of fetal cells into her circulation as well as the egress of her own cells into the fetal circulation. Results of research done so far point to a significant regenerative potential of placental cells that could greatly influence the course of stem cell research together with their role in fetal development. The greatest impact in human and veterinary medicine has human-induced chimerism that implies creation of a unique organism that consists of different genotype cells originating from different species, better known as interspecies chimerism. For many years, scientists have done research on chimerism between evolutionarily close animals, which has led them to discover a great potential for the growth of human cells, tissues and eventually entire organs in the living, animal organism. Such a discovery opened many doors in the field of regenerative medicine as well as made progress in research of human and animal early developmental processes. Although human-animal chimerism holds a lot of hope regarding the progress of science, its research has been extremely slow due to the current legal regulations in the EU as well as whole series of ethical, social and scientific problems.