This book is a pedagogical yet complete introduction to the physics of the one dimension. Recent progress in nanotechnology and material research have made one dimensional systems a crucial part of today's physics. After an introduction to the basic concepts of correlated systems, the book gives a step by step description of the techniques needed to treat one dimension, and discusses the resulting physics. The specific experimental realization of one dimensional systems such as spin chains, quantum wires, nanotubes, organic superconductors, etc., are examined. Given its progressive and pedagogical approach, this book should satisfy both graduate students who want to learn the tools of the trade and become professionals in the field as well as more advanced researchers who want to know more about the physics of a specific one dimensional system without unnecessary technicalities.