Reflecting the major advances that have been made in the field over the past decade‎,‎ this book provides an overview of current models of biological systems‎.‎ The focus is on simple quantitative models‎,‎ highlighting their role in enhancing our understanding of the strategies of gene regulation and dynamics of information transfer along signalling pathways‎,‎ as well as in unravelling the interplay between function and evolution‎.‎ The chapters are self‎-contained‎,‎ each describing key methods for studying the quantitative aspects of life through the use of physical models‎.‎ They focus‎,‎ in particular‎,‎ on connecting the dynamics of proteins and DNA with strategic decisions on the larger scale of a living cell‎,‎ using E‎.‎ coli and phage lambda as key examples‎.‎ Encompassing fields such as quantitative molecular biology‎,‎ systems biology and biophysics‎,‎ this book will be a valuable tool for students from both biological and physical science backgrounds‎.‎