**1. Introduction**

Researchers have been attracted by the mystery of human neural development for hundreds of years. Numerous cellular and animal models have been explored to improve our understanding of neurogenesis in humans for hundreds of years. Although animal models have greatly improved our understanding of neural development, neurological disorders, cortical architecture, and functional regionalization, there are significant differences between the human and rodent brains. For example, the organization and behavior of neural progenitors during embryonic development determine the expansion and folding of the human neocortex to a large degree. Therefore, studying the development of the human brain requires models with human brain characteristics. Organoids are simply, self-organized three-dimensional (3D) tissue cultures that are derived from human pluripotent stem cells (hPSCs), including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), which has gained great interest in simulating tissue development and disease. This technology opens a window to observe some of the most elusive aspects of human biology. Compared with animal models or two-dimensional (2D) cell culture systems, 3D-cultured organoids can overcome the differences between species and closely represent the realistic human-specific development features, which can be utilized to mimic the architecture and functionality of the human tissues, having great advantages in explaining the unique human developmental processes [1, 2]. In the field of neurodevelopment and regenerative medicine, neural organoids replicate human specific features of neurodevelopment, contributing to modeling neurogenesis and neurological diseases [3, 4]. Central nervous system (CNS) injury or damage initiates spatial and temporal neurodegeneration, resulting in irreversible neuronal loss and functional deficits. The vertebrate retina is an extension of the CNS that is composed of seven main types of neurons and glial cells. In recent years, emerging organoidbased research studies of brain and retina have made progress in understanding neural organogenesis, which facilitates successful application of 3D organoid systems in disease modeling and regenerative medicine. In this chapter, we summarize the application of neural organoids of the brain and retina in neurodevelopment and regenerative medicine.
