'Candidatus Phytoplasma prunorum' is an important prokaryotic pathogen that infects stone fruits in Europe. It is known to cause several economically relevant disorders of Prunus spp. which are collectively referred to as European stone fruit yellows (ESFY). This organism is phylogenetically closely related to other important fruit trees pathogens such as apple proliferation (AP), pear decline (PD) and peach yellow leaf roll (PYLR) agents. Together they form a distinct phylogenetic cluster, the AP or 16SrX group. Like the other fruit tree phytoplasmas of the AP group, 'Ca. P. prunorum' exhibits a high host specificity. In nature, this pathogen has been reported to infect only plants in the genus Prunus and to be transmitted by one insect vector species, the psyllid (Psyllidae) Cacopsylla pruni. Also, 'Ca. P. prunorum' includes strains which greatly differ in virulence. This review summarizes the current knowledge of 'Ca. P. prunorum' with emphasis on advances that have been made during the last two decades in understanding molecular and epidemiological aspects. Prospects for disease management and future research which could provide insights into the largely unknown mechanisms involved in pathogenicity of 'Ca. P. prunorum', are also critically discussed.