DNA is both a fundamental building block of life and a versatile natural polymer. Single-molecule force spectroscopy has elucidated the elastic properties of DNA, which facilitate the mechanistic studies of various genome transactions such as packaging, replication, and repair. Moreover, the marriage of single-molecule fluorescence visualization and force manipulation has enabled researchers to directly correlate the tension applied to DNA to the dynamics of DNA-templated processes. In this review, we discuss how our increasing knowledge on DNA mechanics can be harnessed to understand how DNA-binding proteins and DNA-processing enzymes recognize and modify the physical state of DNA to accomplish their biological functions.