The authors have written a nice review on the purposeful use of nonlinearity in vibratory energy harvesting. The current limitations of batteries and advancements in low-power electronic devices are identified as two motivating factors for energy harvesting research. The underlying idea is that vibratory harvesters could replace batteries as a power source or even could enable new technologies. The authors identify the primary limitations associated with linear vibratory harvesters and describe several attempts, along with some of their pitfalls, to overcome these limitations. The article then provides a critical review of recent research focused on the use of nonlinearity to improve the performance of vibratory harvesters.