Understanding the functional communication across brain has been a long sought-after goal of neuroscientists. However, due to the widespread and highly interconnected nature of brain circuits, the dynamic relationship between neuronal network elements remains elusive. With the development of optogenetic functional magnetic resonance imaging (ofMRI), it is now possible to observe whole-brain level network activity that results from modulating with millisecond-timescale resolution the activity of genetically, spatially, and topologically defined cell populations. ofMRI uniquely enables mapping global patterns of brain activity that result from the selective and precise control of neuronal populations. Advances in the molecular toolbox of optogenetics, as well as improvements in imaging technology, will bring ofMRI closer to its full potential. In particular, the integration of ultra-fast data acquisition, high SNR, and combinatorial optogenetics will enable powerful systems that can modulate and visualize brain activity in real-time. ofMRI is anticipated to play an important role in the dissection and control of network-level brain circuit function and dysfunction. In this talk, the ofMRI technology will be introduced with advanced approaches to bring it to its full potential, ending with examples of dissecting whole brain circuits associated with neurological diseases utilizing ofMRI.