NMDA receptors (NMDARs) are a subtype of ionotropic glutamate receptors that mediate excitatory neurotransmission and synaptic plasticity in the brain. NMDARs play important roles in various normal brain functions such as learning, memory, and cognition, but also contribute to the pathogenesis of several developmental, neurological, and psychiatric disorders. Alterations in NMDARs can result in either hypo- or hyperfunction of NMDARs, which can impair neuronal viability, synaptic efficacy, and network oscillations. In this review, we summarize the current knowledge on the involvement of NMDA receptors in Alzheimer’s disease, autism spectrum disorder, epilepsy, and schizophrenia. We also highlight the potential therapeutic strategies that target NMDAR modulation and dysfunction in these disorders.