It has been more than 50 years since the elucidation of the structure of double-helical DNA. Despite active research and progress in DNA biology and biochemistry, much remains to be learned in the field of DNA biophysics. Predicting the sequence-dependent curvature and flexibility of DNA is difficult. Applicability of the conventional worm-like chain polymer model of DNA has been challenged. The fundamental forces responsible for the remarkable resistance of DNA to bending and twisting remain controversial. The apparent 'softening' of DNA measured in vivo in the presence of kinking proteins and superhelical strain is incompletely understood. New methods and insights are being applied to these problems. This review places current work on DNA biophysics in historical context and illustrates the ongoing interplay between theory and experiment in this exciting field.