Since best level 4 evaluation publish in the 1959 , it has become the industry standard of the evaluation of training effect. However, the best level 4 effect evaluation is widely misused and misunderstood. It happened in the 50th anniversary of its launch,this book will accurately describe the development of best level 4 evaluation and provide the main principle and method for the complete application of the best level 4 model in modern society. The first four original articles on the best level 4 effect evaluation are also collected in the book. The founder of the best level 4 evaluation, Donald Kirkpatrick, will personally tell you in the book that where this method came from and how it got a great development under the help of Jack Phillips etc. This book includes the most detailed explanation about the basic principles so far.