Oligodendroglia are cells responsible for creating myelin sheaths for axons in the CNS. However, pathologies of oligodendroglia other than demyelination are not well understood due to the lack of adequate methods of characterizing pathological conditions affecting oligodendroglia in human tissue. This review discusses three major topics with the aim of clarifying some of the controversies in the study of oligodendroglia. The oligodendroglioma, a relatively indolent form of diffuse gliomas thought to originate in oligodendrocytes, has never demonstrated myelin formation on electron microscopy nor shown a constant expression of myelin‐related proteins. Oligodendrogliomas instead share an immune phenotype with oligodendrocyte progenitor cells (OPCs). Another type of cell that resembles OPCs are oligodendroglia‐like cells (OLCs), which occur in many types of low‐grade tumors and focal cortical dysplasia. In neurodegenerative disorders, oligodendroglia can be a target of abnormal aggregations of proteins such as tau. Tau‐positive oligodendroglial inclusions in progressive supranuclear palsy and corticobasal generation differ from each other morphologically, ultrastructurally and biochemically, suggesting disparate underlying pathological processes despite significant overlapping of the clinical manifestations. To promote the study of oligodendroglia, novel methods for detecting OLCs in situ are urgently required.