DNA topology and geometry Linking number, writhe, twist The theorem of Calugareanu and White, DNA supercoiling Methods for calculating and estimating writhe Surface linking number, linking number paradox DNA knots and catenanes, topoisomerases, recombination DNA elasticity Idealized elastic rod model, equilibrium configurations, supercoiling of rings, bifurcations Elastic rod models with intrinsic curvature, kinetoplast DNA Higher order continuum models, kinkable DNA Base-pair level models, sequence-dependence of DNA elasticity DNA looping, role of looping in transcription regulation Electrostatic effects