Difference between Session and HttpContext.Current.Session

There is no difference.

The getter for Page.Session returns the context session.

Nothing. Session just points to the HttpContext.Current.Session.

Internally, Page.Session points to It's HttpContext.Current.Session only, but there are still two differences depending on from where it's called.

Page.Session can be accessed only from classes inherited from System.Web.UI.Page and it will throw HttpException when accessed from WebMethod.
Where as HttpContext.Current.Session can be accessed from anywhere as long as you're running in the context of a web application.


Other important difference where you can access Page.Session but cannot access HttpContext.Current.Session :

If there is a method named GetData in your page(inherited from System.Web.UI.Page) which is executed concurrently in different threads from some other page method, GetData method can access the Page.Seession, but you cannot access HttpContext.Current.Session.

It's because GetData has been called from different thread so HttpContext.Current is null and HttpContext.Current.Session will throw null reference exception, but Page.Session will still be attached with page object so page method GetData can access the Page.Session.