Embrittlement is a series complex mechanism that is not completely understood. The mechanisms can be driven by temperature, stresses, grain boundaries, or material composition. However, by studying the embrittlement process, preventative measures can be put in place to mitigate the effects. There are several ways to study the mechanisms. During metal embrittlement (ME), crack-growth rates can be measured. Computer simulations can also be used to enlighten the mechanisms behind embrittlement. This is helpful for understanding hydrogen embrittlement (HE), as the diffusion of hydrogen through materials can be modeled. The embrittler does not play a role in final fracture; it is mostly responsible for crack propagation. Cracks must first nucleate. Most embrittlement mechanisms can cause fracture transgranularly or intergranularly. For metal embrittlement, only certain combinations of metals, stresses, and temperatures are susceptible. This is contrasted to stress-corrosion cracking where virtually any metal can be susceptible given the correct environment. Yet this mechanism is much slower than that of liquid metal embrittlement (LME), suggesting that it directs a flow of atoms both towards and away from the crack. For neutron embrittlement, the main mechanism is collisions within the material from the fission byproducts.