The triboelectric effect (TE), simply described as the generation of electricity from tribology or friction, has been known for over 1500 years. TE arises from charge transfer between surfaces under contact, typically attributed to electron transfer. However, emerging understanding shows how the ion transfer and material transfer (bond cleavage) mechanisms play a key role in TE. An engineering focus on increasing the porosity, surface roughness, and use of heterogeneous materials has resulted in a recent explosion in triboelectric literature, particularly toward soft and flexible polymer devices. Here, we critically evaluate recent progress in TE generators and link engineered performance to the fundamental driving forces of triboelectricity using the exemplar triboelectric polymer poly(dimethylsiloxane).