Organizational structures provide hierarchy and define functions within an organization. There are four main types of structures: bureaucratic, functional, divisional, and matrix. Bureaucratic structures maintain strict hierarchies and come in three forms - pre-bureaucratic lacking standards, bureaucratic with some standardization, and post-bureaucratic following modern ideas while keeping hierarchies. Functional structures divide the organization into functional groups like marketing, IT, etc. Divisional structures separate the organization into independent divisions based on products, services, or geography. Matrix structures combine functional and divisional forms by placing employees in both functional groups and product/project divisions.