TWENTY YEARS BULGARIAN-SERBIAN COOPERATION IN ASTRONOMY: JOINT ASTRONOMICAL CONFERENCES Milcho Tsvetkov(1,3), Milan Dimitrijevic(2), and Katya Tsvetkova(3) 1) Astronomical Institute with National Astronomical Observatory, Bulgarian Academy of Sciences, Tsarigradsko Sh. Blvd 72, 1784 Sofia, Bulgaria 2) Belgrade Astronomical Observatory, Volgina 7, 11060 Belgrade, Serbia 3) Institute of Mathematics and Informatics, Bulgarian Academy Sciences, Acad. G. Bonchev Str. Bl.8, 1113 Sofia, Bulgaria Invited talk) Abstract. Since 1998 a regular joint conferences initiative between Bulgarian and Serbian astronomers has been established. On bilateral basis joint meetings were organized: Bulgarian-Serbian ones if the meeting is held in Bulgaria or Serbian-Bulgarian if it was organized in Serbia and in both cases with the support of the Bulgarian and Serbian Academies of Sciences and Art (BAS and SANU). During first 10 years 5 joint conferences were organized described in details in the paper of Milan Dimitrijevic and Milcho Tsvetkov (2009). Here we stress on the second 10 years period (2010-2018) when 5 more conferences were organized - in Belgrade (2008), Chepelare (Bulgaria, 2010), Lescovac (Serbia, 2012), Sofia (2014), and Belgrade (Serbia, 2016). This collaboration started on a basis of private friendly relationships enlarges later officially in many agreements between both institutes: Institute of Astronomy and National Astronomical observatory (BAS) and Belgrade Astronomical observatory (BAO). Over the years the bilateral conferences become more and more popular and many astronomers from other countries (Czech Republic, Russia, Germany, Ukraine, France, etc.) also attended the meetings. This collaboration was extended to several joint astronomical initiatives as the COST action TD1403, the supported by UNESCO Regional Bureau for Science and Culture in Europe (UNESCO-BRESCE), Eurasian Astronomical Society (EAAS), etc. We also extended the topics to the modern field in Astronomy as Astroinformatics. This already traditional collaboration once more emphasizes the significance of the development and enlargement of the Bulgarian-Serbian joint work in Astronomy, Space Sciences and Astroinformatics. Milan S. Dimitrijevic, Milcho Tsvetkov, Публ. Астр. друш. “Руђер Бошковић” бр. 8, 2009, pp. 795-811, Зборник радова конференције “Развој астрономије код Срба V” Beograd, 18-22 April 2008, Ed. M. Dimitrijevic. http://www.wfpdb.org/ftp/0_MISCELLANEOUS_AOB/DAAS_5/pdfs-s/66.pdf)