The success of brain-computer interfaces (BCI) systems is largely dependent on the ability to record and interpret clear neurophysiological signals invasively or noninvasively through the scalp and skull. In particular, two noninvasive techniques of recording neurophysiological signals namely electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS) have been extensively used in BCI research. In this chapter, we provide an overview of the underpinning physiology of EEG and fNIRS signals and the application of both techniques in BCI research. We further discuss the inherent limitation of EEG and fNIRS in BCI research and potential solutions of addressing these limitations.