In ASP.NET, View State is a feature that allows server-side controls to persist their state across postbacks (when a page is submitted to the server for processing). It is a hidden field on the web page that stores information about the state of the controls on the page.

The primary purpose of View State is to allow server-side controls to maintain their state and values across postbacks so that users can interact with the page without losing any data. For example, if a user fills out a form on a web page and clicks a button to submit the form, the data entered into the form is stored in View State and can be retrieved when the page is submitted to the server.

ViewState is enabled by default in ASP.NET Web Forms but can be disabled or customized as needed. It is important to note that ViewState can significantly increase the size of a page, which can impact performance, especially if the page contains large amounts of data. Therefore, it is recommended to use ViewState only when necessary and to minimize its use wherever possible.