Antonie van Leeuwenhoek opened up a whole new world to us; he was the first to observe bacteria and other microscopic lifeforms which could not be seen by the naked eye. He is now regarded as the father of microbiology and yet he had neither scientific training nor university education, and spent his life first as a linen merchant and then a civil servant in a small Dutch city. To understand quite how game-changing Leeuwenhoek’s discoveries were, you have to imagine a world where just about everyone on the planet could only see things that were within the range of unaided human eyesight. Magnifying glasses were the preserve of a privileged few, and other optical instruments, such as simple telescopes and microscopes, were rarer still. So it’s little wonder that Leeuwenhoek was met with disbelief when he claimed that he had seen bustling, vibrant lifeforms in what for everyone was just a drop of clear, pure water. To find out how this extraordinarily curious Dutchman arrived at his discoveries, Rajan Datar is joined by Elisabeth Entjes who is one of the editors of Leeuwenhoek’s Collected Letters, Tiemen Cocquyt who as curator at the Boerhaave Museum of the history of science in Leiden has a special interest in Leeuwenhoek’s microscopes, and by biochemist and writer Nick Lane who is professor of Evolutionary Biochemistry at University College London. (Photo: Antonie van Leeuwenhoek's microscope. Credit: Rijksmuseum Boerhaave)