“The role of the infinitely small in nature is infinitely great.” (Louis Pasteur) The world is much more than you can see! There is an invisible multitude of microorganisms which are our life support. Discovering, recognizing and exploring the importance of microorganisms is a long road that is not yet appreciate by all. The aim of creating the Day of the Microorganism is to raise awareness among young people and society in general of the role of microorganisms as life supporting systems and biotools. At the initiative of Portuguese Society of Microbiology, on September 17, 2018, across Europe and the world for the first time was celebrated the International Microorganism Day. The 17th of September was chosen to celebrate the day when the Dutch scientist Anton van Leeuwenhoek, in 1683, has sent a letter to the Royal Society of London making him the first person to observe and describe single-celled organisms, thereby launching the basis for Microbiology, one of the most important branches of Life Sciences. Starting from 2018, September 17 is an open day for everyone who is passionate about the fascinating world of microscopic organisms. The Institute’s laboratories are open to visitors - everyone is welcome! During the visit you will get acquainted with the Collection of non-pathogenic microorganisms and will perform microbiology lab routine activities.