Book excerpt: An accessible introduction to the history, fundamental concepts, challenges, and controversies of the fMRI by one of the pioneers in the field. The discovery of functional MRI (fMRI) methodology in 1991 was a breakthrough in neuroscience research. This non-invasive, relatively high-speed, and high sensitivity method of mapping human brain activity enabled observation of subtle localized changes in blood flow associated with brain activity. Thousands of scientists around the world have not only embraced fMRI as a new and powerful method that complemented their ongoing studies but have also gone on to redirect their research around this revolutionary technique. This volume in the MIT Press Essential Knowledge series offers an accessible introduction to the history, fundamental concepts, challenges, and controversies of fMRI, written by one of the pioneers in the field. Peter Bandettini covers the essentials of fMRI, providing insight and perspective from his nearly three decades of research. He describes other brain imaging and assessment methods; the sources of fMRI contrasts; the basic methodology, from hardware to pulse sequences; brain activation experiment design strategies; and data and image processing. A unique, standalone chapter addresses major controversies in the field, outlining twenty-six challenges that have helped shape fMRI research. Finally, Bandettini lays out the four essential pillars of fMRI: technology, methodology, interpretation, and applications. The book can serve as a guide for the curious nonexpert and a reference for both veteran and novice fMRI scientists.