Pulsar wind nebulae (PWNe) are some of the brightest sources in the very high energy sky and their gamma-ray emission, powered by relativistic electrons, provides a direct view of some of the most extreme Galactic environments. Even though PWNe like the Crab are some of the most well-known and widely studied objects in the high energy sky, little is understood about their nature. In particular, we lack clear characterizations of the injected particles and their consequent evolution once inside the nebula. Taking advantage of the recent upgrades to the Fermi-LAT and using Fermi observations with over 11.5 years of data, we are performing a systematic search for MeV - GeV PWNe. This systematic effort targets both known Fermi pulsars, in search of their PWN companions, as well as the gamma-ray counterparts of PWNe discovered at other wavelengths. Studies of the PWN emission structure over the entire electromagnetic spectrum offer the best way to understand the particle injection spectrum, its evolution, and the nature of the particle population that is eventually injected into the ISM. A combination of observational studies with semi-analytic modeling efforts may provide an intimate view of the nature and evolution of PWNe.