In ASP.NET pages, the view state represents the state of 
the page when it was last processed on the server. It's 
used to build a call context and retain values across two 
successive requests for the same page. By default, the 
state is persisted on the client using a hidden field added 
to the page and is restored on the server before the page 
request is processed. The view state travels back and forth 
with the page itself, but does not represent or contain any 
information that's relevant to client-side page display. In 
this column, I'll take a tour of the view state 
implementation in ASP.NET and show how to keep your Web 
pages fit and trim and a bit more secure.

it is the internal structure, automatically retains value 
of the controls in the hidden fields on the page.

It is the process of maintaing controls data under postback 
implimentation.It can be implimented by using Hidden field.

ViewState is a concept of maintaining controls properties 
under postback implementation.it can be implemented in the 
form of hidden field.