This volume covers the latest developments in optical imaging of the brain which is becoming an increasingly important functional neuroimaging method. Optical intrinsic signals offer unrivaled temporal and spatial resolution of functional measurements of the exposed brain cortex in animals and humans. Near-infrared spectroscopy and imaging ap­ proaches permit the noninvasive functional assessment of the human brain at bedside. Main advantages of these optical techniques are the biochemical specificity of the meas­ urements and the potential of measuring correlates of intracellular and intravascular oxy­ genation simultaneously. Recent data indicate that one may also measure a more direct correlate of neuronal activity associated with changes in light scattering. In this volume, recent technical progress of the optical method is covered as well as the physiological basis of the measurements. In simultaneous studies, near-infrared spec­ troscopy measurements are directly compared to other functional methods, especially PET and fMRI and examples are given for new applications of the NIRS-method. Based on re­ sults obtained with optical methods and other functional techniques the latest in our under­ standing of the coupling of neuronal activity and cerebral blood flow response is reviewed. This is an important basis for a better understanding of all functional neuroi­ maging methods which rely on neurovascular coupling such as PET, SPET and fMRI. Fi­ nally the optical method is put into the perspective of presently available functional neuroimaging methods including fMRI, PET, MEG and EEG.