Open Source Day is an international conference gathering fans of open solutions from Central and Eastern Europe. Mission of the event is to introduce open source solutions to Polish public and business institutions and popularize it as a secure, efficient, cost saving alternative to proprietary software. The conference has taken place in Warsaw since its beginning in 2007. Participants are mainly managers, developers, technical officers of public, banking, and insurance industries. The conference has become a platform for exchanging experience, contacts and use cases of open source solutions in fields of: virtualization, cloud computing, database, big data, Information security. Promotion of Open Source software Founders of the conference believe that by making open software popular they might initialize local communities as well as give start to small businesses in Poland which would provide support and develop open source solutions locally. Due to its role in promoting Open Source software in wider business and public applications, the Open Source Day Conference won support from public administration and were operated under the auspices of: Ministry of Education, Ministry of Administration and Digitization, Ministry of Economy and European Commission as well. History Open Source Day was launched in 2007 by a handful of open source enthusiasts. They wanted to inform the public about the opportunities open software provides for market. Initial event drew only a moderate number of participants. Since then however each consecutive edition the event has grown in scope of subjects as well as the size of auditorium. Open Source Day 2008 The first full-fledged conference of Open Source Day took place on 9 April in Radisson SAS Hotel, Warsaw. Seven sessions were organized on different open source successful implementations in public administration: French project Copernic, city administration of Vienna and Swedish Police. Technical presentation were dealing with open source project: Xen, SELinux (Security Enhanced Linux), Metamatrix and SOA. Open Source Day 2009 The 2nd Open Source Day Conference took place on 6 May 2009 in the Radisson Blu Sobieski Hotel in Warsaw. 350 attendees participated. The event was supported by main technological partners Red Hat and IBM. Technical sessions covered: enterprise-class Linux distributions, virtualization, application servers and SOA platforms as well. Open Source Day 2010 The 3rd Open Source Day Conference came about on 12 May 2010 in the Palace of Culture and Science in Warsaw. The event gathered 400 guests and was supported by 12 technology vendors and 5