Modeling is now one of the most efficient methodologies in lifesciences. From practice to theory, this book develops this approachillustrated by many examples; general concepts and the currentstate of the art are also presented and discussed.An historical and general introduction informs the reader howmathematics and formal tools are used to solve biological problemsat all levels of the organization of life. The core of this bookexplains how this is done, based on practical examples coming, forthe most part, from the author's personal experience. In mostcases, data are included so that the reader can follow thereasoning process and even reproduce calculus. The final chapter isdevoted to essential concepts and current developments. The mainmathematical tools are presented in an appendix to the book and arewritten in an adapted language readable by scientists,professionals or students, with a basic knowledge ofmathematics.