The first edition of this book was published in 1966 and became an instant classic text. The third edition waspublished in 2000 authored by Professors Southwood and Henderson. The availability of computer programs for many aspects of analysis of ecological data has continued to transform the way ecologists work. This has resulted in some important changes in the 4th edition. Many of the computational methods described in detail in the 3rd edition have been replaced with a description of the available software with brief descriptions of use and where to obtain it. In particular, reference is made to procedures available in R and other freely available software systems. There are additional references to web resources including equipment suppliers, software downloads and detailedmethodologies.