Abstract: The growth of isolated ionized regions during the early stage of reionization is well described by the “bubble model”. However, the basic assumption of isolated and spherical ionized bubbles does not apply after the percolation of HII regions. In this talk, I will introduce the “island model” which describes the nature and distribution of large neutral regions during the late epoch of reionization. The neutral islands refer to the large-scale under-dense regions where fewer galaxies formed and hence ionized later, and they are modeled in the excursion set framework taking into account the ionizing background after the percolation. I’ll present the basic idea and main results of the analytic island model and a set of semi-numerical simulation, islandFAST. Also, I’ll talk about our recent work on modeling the global 21 cm signal from the cosmic dawn.