Polymer electrolyte membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) technology represent promising low-temperature electrochemical power generation technologies that operate on hydrogen and methanol respectively. These technologies have attracted intense worldwide commercialization research and development efforts with a large element of these efforts directed at materials developments for fuel cell durability and long term operation.This two volume set presents a comprehensive and detailed review of the fundamentals, performance, and in situ characterization of PEMFCs and DMFCs.ย Volume 2 details in situ characterization, including experimental and innovative techniques used to understand fuel cell operational issues and materials performance. The opening section reviews enhanced techniques for characterization of catalyst activities and processes, such as X-ray absorption and scattering, advanced microscopy and electrochemical mass spectrometry. Chapters in part two review characterization techniques for water and fuel management, including neutron radiography and tomography, magnetic resonance imaging and Raman spectroscopy. The conclusion focuses on locally resolved characterization methods, from transient techniques and electrochemical microscopy, to laser-optical methods and synchrotron radiography.