Magnetic force spectroscopy is a rapidly developing single molecule technique that has found numerous applications at the interface of physics and biology. Since the invention of the first magnetic tweezers, a number of modifications to the approach have helped to relieve the limitations of the original design while amplifying its strengths. Inventive molecular biology solutions further advanced the technique by expanding its possible applications. In its present form, the method can be applied to both single molecules and live cells without resorting to intense irradiation, can be easily multiplexed, accommodates multiple DNAs, displays impressive resolution, and allows a remarkable ease in the stretching and twisting of macromolecules. In this review, we describe the architecture of magnetic tweezers, key requirements for experimental design and analysis of data, and outline several applications of the method that illustrate its versatility.