Myelinoids or myelin organoids are three dimensional in vitro cultured model derived from human pluripotent stem cells (hPSCs) that represent various brain regions, spinal cord or the peripheral nervous system in early fetal human development. They have the capacity to recapitulate aspects of brain developmental processes, microenvironments, cell to cell interaction, structural organization and cellular composition. The differentiating aspect dictating whether an organoid is deemed a cerebral organoid/brain organoid or myelinoid is the presence of myelination and compact myelin formation that is a defining feature of myelinoids. Due to the complex nature of the human brain, there is a need for model systems which can closely mimic complicated biological processes. Myelinoids provide a unique in vitro model through which myelin pathology, neurodegenerative diseases, developmental processes and therapeutic screening can be accomplished. Myelinoids are a newly emerging model, however, studies have already demonstrated their potential in disease modeling, genome analysis, and therapeutic evaluation. History In vitro models have been a critical component of many biological studies. Monolayers, or 2D cultures, have been widely used in the past, however, they are limited by their lack of complexity and fail to recapitulate tissue architecture involved in biological processes occurring in vivo. Model organisms, such as Mus musculus, Caenorhabditis elegans, Drosophila melanogaster, and Saccharomyces cerevisiae, recapitulate biological complexity better than 2D monolayer cultures. However, these model organisms do not perfectly capture human biology. Specifically, there are stark differences in brain development between mice and humans. Major developmental differences include variability in division patterns of neural stem cells and localization and types of glial cells that occur at specific stages in development. Leveraging pluripotent stem cell technologies, brain organoids and cerebral organoids were developed to fill the gap in model systems to study human specific brain development and pathology in vitro. The first cerebral organoid was established in 2013 by Lancaster et al. Since then, various protocols have emerged for generating organoids for different brain regions such as cerebellar, midbrain, hippocampal, forebrain, and hypothalamic organoids. Cerebral organoids provide a neurological model through which diseases, development and therapeutics can be studied. However, a major constraint of cerebral organoids is that they lack robust myelin formation and are therefore not well suited to studies investigating white matter. Madhavan et al., recognized this limitation of cerebral organoids. In 2018, Madhavan et al., generated brain organoids containing a population of myelinating oligodendrocytes.The process of generating these myelinated brain organoids