It is now almost 20 years since the journal Fluctuation and Noise Letters (FNL) was first published, and hence this book is to commemorate what is an important milestone. It consists of 55 reprinted articles from the first 20 years of FNL, together with a short Introduction explaining their context and significance. In choosing the papers, the Editors have paid some regard to citation counts, but were guided mainly by the perceived interest and scientific importance of the work. The selected articles are arranged across eight themes.