This is the first publication of the two most important notebooks created by William Henry Fox Talbot (1800–1877), the inventor of negative/positive photography. Henry Talbot preserved the 18th century tradition of the gentleman amateur scientist in the face of increasing professionalisation of science and technology in the 19th century. He had great powers of imagination and often conceived of things well beyond his present ability to execute. Notebooks P and Q span the period from the first public announcement of photography in 1839 through the 1843 plateau of Talbot's researches. They record both his false starts and his triumphs. While the emphasis is on the new art of photography, there is substantial reference to chemistry, electricity, light, optics and railroad motive power. The notebook pages are reproduced in full, preserving the tempo and organisation of Talbot's thoughts, and keeping his sketches in context. A full expanded transcription decodes Talbot's sometimes difficult hand and abbreviations. Extensive notes and scholarly apparatus interpret and establish the context of Talbot's work.