Meningitis, encephalitis, and encephalomyelitis are terms used to describe inflammatory conditions of the meninges, brain, or brain and spinal cord, respectively. These inflammatory processes frequently occur concurrently, with the terms meningoencephalitis and meningoencephalomyelitis used. Although such conditions have long been associated with bacteria, viruses, fungi, rickettsial agents, and parasites, more recent findings in both people and animals are starting to also implicate chemical agents and immune-mediated processes, with genetic predispositions proposed for some of these latter conditions. Depending on the causal agent, the extent and speed of onset, and location of the inflammation, clinical signs can vary from subtle to dramatic, and therapies can have varied successes. Accurate diagnosis is dependent on quality neurologic (including ocular) examinations and supported by CSF analysis and imaging, in particular MRI. In unsuccessful cases, the importance of postmortem examinations cannot be underestimated, because historically, many zoonotic agents have manifested as meningoencephalitis in people and animals.