Ljungan virus (LV) is a recently identified picornavirus of the genus Parechovirus. LV has been isolated from voles trapped in Sweden and also in the United States. LV infected small rodents may suffer from diabetes type 1 and type 2 like symptoms, myocarditis and encephalitis. LV has been proposed as a human pathogen, with indications of causing diabetes type 1, myocarditis and intrauterine fetal deaths. In this thesis, cell culture adapted LV strains were utilised for development and adaptation of several basic methodological protocols to study the LV biology, e.g. real time PCR, highly specific antibodies and a reverse genetics system. These methods allowed detailed studies of this virus and how it interacts with the host cell. The genomic 5'-end was identified and modelling showed unique secondary structure folding of this region. The LV encodes an aphthovirus-like 2A protein with a DvExNPGP motif. This motif was found to mediate primary cleavage of the LV polyprotein in vitro and is proposed to constitute the carboxy terminus of the structural protein VP1 in LV. Rabbit polyclonal antibodies generated against recombinant structural proteins were used to verify that the LV virion is composed of the structural proteins VP0, VP1 and VP3. Cell culture studies showed that LV replicates to low titer with an absent or delayed cell lysis. LV is proposed to be able to spread by a, for picornaviruses, not previously demonstrated direct cell-to-cell transmission. All results taken together suggest a maintenance strategy of LV including low amounts of the LV genome and persistently infected hosts. Stability studies showed that the LV virion not only maintain activity in acidic and alkaline environments but also exhibit resistance to the commonly used disinfectant Virkon®.The results presented in this thesis show that LV has several unique properties, not previously observed for a picornavirus.