The visual work of Otto Neurath and his associates, now commonly known as Isotype, has been much discussed in recent years. This short book explains its essential principles: the work of ‘transforming’, or putting information into visual form. This deeper level of their work – which is applicable in all areas of design – is routinely neglected in the assumption that Isotype is just a matter of symbols and pictograms. At the core of the book is a previously unpublished essay by Marie Neurath, the principle Isotype transformer, which she wrote in the last year of her life. This is supplemented by Robin Kinross with commentary on illustrated examples of Isotype and other supporting short essays.