D-Serine, a co-agonist of NMDA receptors has sparked a contentious debate within the scientific community regarding its status as a gliotransmitter or a neurotransmitter. This comprehensive review delves into the heart of this debate, offering a meticulous analysis of the existing evidence from various research methodologies. Immunostaining studies and cell-selective mutations provide compelling support for D-serine's neuronal origin, bolstering the serine shuttle model. In contrast, the gliotransmission hypothesis, proposing astrocytic synthesis and release, faces critical scrutiny as inconsistencies in supporting data emerge. In vivo microdialysis experiments unveil a neuronal contribution to D-serine release and its profound impact on synaptic plasticity, further strengthening the case for neuronal dominance. Counterarguments in favor of astrocytic D-serine release are systematically dissected, revealing inherent limitations and ambiguities. Collectively, the evidence corroborates D-serine's neuronal source and discounts the astrocytic hypothesis. This review underscores the need for scientific rigor when evaluating contentious topics and affirms the simplicity of the neuronal explanation, aligning D-serine with the serine shuttle model, thus advancing our comprehension of its pivotal role in synaptic function and cognitive processes. As the debate continues to evolve, this exploration encourages ongoing research to unravel the intricate mechanisms governing D-serine neurotransmission.