On the basis of our analysis of detailed measurements of the dependence of the overstretching transition of double-stranded DNA (dsDNA) on temperature, pH, and ionic strength, we have demonstrated that a model of force-induced melting accurately describes the thermodynamics of DNA overstretching. Measurements of this transition allow us to determine the stability of dsDNA and obtain information similar to that obtained in thermal melting studies. This single-molecule technique has the advantage that it can be used to measure DNA stability at any temperature. We discuss the use of this technique to study the nucleic acid chaperone activity of the HIV-1 nucleocapsid protein.