This lecture covers the principles and applications of Energy Dispersive Spectroscopy (EDS) and Environmental Scanning Electron Microscopy (ESEM). Topics include x-ray detection, electron emission, x-ray creation, ionization efficiency, Moseley's law, x-ray generation rate, and detector technologies. The ESEM section discusses sample environments, differential pumping in vacuum systems, beam diffusion, charge neutralization, and imaging insulating samples.