What is life? What type of system is life? How can we understand life? Or what does "understanding life" really mean? Sixty years since the publication of What Is Life? by Schrodinger ¨ and after the rise and success of molecular biology, have we reached the answer to these questions? In the recent years, I have often been asked by young researchers and students in biology: "I am afraid that such basic questions on a life system itself are not answered by the main-stream approach of c- rent biology that elucidates molecules and genes. We need some alternative approach. WhatamItodo?"Theyaresatis?edneitherwiththecurrenttrend in bioinformatics nor with the detailed computer models, and are striving for a framework complementary to molecular biology, a one that does not rely on enumerative approach. Responding to these voices, I have explained approaches my colleagues and I have been taking both theoretically and experimentally, in lectures and seminars. Although they show much interest, introduction of these rather interdisciplinary style of research is not easy, let alone discussing how we can understand life. Of course they ask for some books that describe a theoretical basis of our approach and the summaries of the recent studies. My desire to answer these requests from the students and researchers was the main force that had driven me to write the present book. On the other hand, those working in nonlinear dynamics and theoretical physicshavestrivedtosetupanoveltheoreticalframeworkthatiscompatible with biological systems.