This book provides the basis for understanding the elastic properties of nucleic acids (DNA RNA) the methods used to manipulate them (e.g. optical magnetic and acoustic tweezers and traps) and how to observe their interactions with proteins (e.g. fluorescence microscopy FCS FRET etc.). It then exemplifies the use of these various methods in the study of three families of DNA enzymes: polymerases helicases and topoisomerases. The book aims not to be exhaustive but rather to stimulate the imagination of readers in the application of these single molecule approaches to the study of DNA/RNA and their interactions.<br>