This is an update of the Reprints and Introduction volume on Chaos first published in 1984. The general layout remains the same: an Introduction, followed by a collection of reprinted papers, and a Bibliography on chaos. The Introduction, while preserving its comprehensive yet elementary style, reflects recent developments in the field such as characterization of chaotic attractors by using experimental time series and the thermodynamic formalism of describing fractals. From the selected papers only less than one-third have been kept, the majority has been replaced by more recent research articles or reviews, including reviews on chaos in chemistry, biology, ecology and economy. In addition, the Bibliography has been extended to more than 2200 titles. On the whole, the volume is designed to be a source book for those entering the field of chaotic dynamics. The readership covers various branches of physical sciences and engineering. It may be used as a text book for graduate students as well.