The generation of cortical dynamics in awake mammals is not yet fully understood. However, it is known that neurons leverage distinct organizational schemes to achieve behavior and cognitive function, and that this precise spatiotemporal organization may go awry in illness. In 2003, a form of scale-free synchrony termed “neuronal avalanches” was first observed by Beggs & Plenz in cultured cortical tissue and later confirmed in rodents, nonhuman primates, and humans. In this dissertation, we draw from monkey and rodent studies to demonstrate that neuronal avalanches capture key features of neural population activity and constitute a robust and stable (e.g. self-organized) indicator of balanced excitation and inhibition in cortical networks. We also show for the first time that neuronal avalanches and oscillations co-exist in frontal cortex of nonhuman primates and identify the avalanche temporal shape as a biomarker predicated upon critical systems theory. Finally, we present progress towards characterizing altered avalanche dynamics in a developmental mouse model for schizophrenia using 2-photon calcium imaging in awake animals.