Magnetoencephalography (MEG) is a neuroimaging technique that has excellent temporal as well as good spatial resolution for measuring neural activity and has been extensively employed in cognitive neuroscience. However, MEG has only been more recently applied to investigations of brain networks and biomarkers in psychiatry. Besides providing new insights into the pathophysiology of major psychiatry syndromes, especially in schizophrenia, a major objective of current research is the identification of biomarkers that could inform early intervention and novel treatments. This chapter will provide a state-of-the-art overview of MEG as applied to schizophrenia, autism spectrum disorders, and Alzheimer's disease, summarizing methodological approaches and studies investigating alterations during resting-state and task-related paradigms. In addition, we will highlight future methodological developments and their potential for applications of MEG in psychiatry.