Functional magnetic resonance imaging (fMRI) measures quick, tiny metabolic changes that take place in the brain, providing the most sensitive method currently available for identifying, investigating, and monitoring brain tumors, stroke, and chronic disorders of the nervous system like multiple sclerosis, and brain abnormalities related to dementia or seizures. This overview explains the principles of fMRI, scanning methodlogies, experimental design and data analysis, and outlines challenges and limitations of fMRI. It also provides a detailed neuroanatomic atlas, and describes clinical applications of fMRI in cognitive, sensory, and motor cases, translating research into clinical application.