Functional magnetic resonance imaging (fMRI) based on blood-oxygenation-level-dependent contrast has been widely used for detecting neural activity in the cortex of the human brain. Recently there has been growing interest in detecting and characterizing fMRI signals in white matter (WM) and applying fMRI of WM to clinical studies, which signifies a paradigm shift for brain fMRI research. In this talk, the historical background of WM fMRI is first briefly reviewed, with focus on resting state acquisitions, along with supporting evidences from various laboratories. The current major developments in studies of biophysical mechanisms of WM fMRI and clinical and neuroscience applications are then summarized. Finally, directions for future research in this area and potential technical challenges are discussed.