The first chapter establishes who practised architecture in the period and on what grounds they were considered to be credible practitioners of architectural design. Initially I set out the nature of the various people who designed buildings in the period and focus on one particularly important group who I term autodidactic architects, on the grounds that their credibility as architects came from their own learning from various sources. I then explore two authors who wrote extensively on this figure: Roger North, who defined the autodidactic architect in moral terms, and John Evelyn, who provided a more pragmatic definition of what he called the Architectus Ingenio. Evelyn, in contrast to North, claimed that people who had previously been builders could be included in the category of intellectual architect. This discussion sets up the rest of the book, which explores the nature of the knowledge these figures were expected to handle.