ASP solves this problem by creating a unique cookie for each user. The cookie is sent to the client and it contains information that identifies the user. This interface is called the Session object.

The Session object is used to store information about, or change settings for a user session. Variables stored in the Session object hold information about one single user, and are available to all pages in one application. Common information stored in session variables are name, id, and preferences. The server creates a new Session object for each new user, and destroys the Session object when the session expires.

When does a ASP Session Start?
A ASP session starts when:

A new user requests an ASP file, and the Global.asa file includes a Session_OnStart procedure
A value is stored in a Session variable
A user requests an ASP file, and the Global.asa file uses the <object> tag to instantiate an object with session scope

When does a Session End in ASP?
An ASP session ends if a user has not requested or refreshed a page in the application for a specified period. By default, this is 20 minutes.

If you want to set a timeout interval that is shorter or longer than the default, you can set the Timeout property.

The example below sets a timeout interval of 5 minutes:

<%
Session.Timeout=5
%>

To end a session immediately, you may use the Abandon method:

<%
Session.Abandon
%>

Note: The main problem with sessions is WHEN they should end. We do not know if the user's last request was the final one or not. So we do not know how long we should keep the session "alive". Waiting too long for an idle session uses up resources on the server, but if the session is deleted too soon the user has to start all over again because the server has deleted all the information. Finding the right timeout interval can be difficult!

Tip: If you are using session variables, store SMALL amounts of data in them.

ASP Store and Retrieve Session Variables
ASP Session object can store variables in it.

The example below will set the Session variable username to "Mickey Mouse" and the Session variable age to "50":

<%
Session("username")="Mickey Mouse"
Session("age")=50
%>

When the value is stored in a session variable it can be reached from ANY page in the ASP application:

Welcome <%Response.Write(Session("username"))%>

The line above returns: "Welcome Mickey Mouse".

You can also store user preferences in the Session object, and then access that preference to choose what page to return to the user.

The example below specifies a text-only version of the page if the user has a low screen resolution:

<%If Session("screenres")="low" Then%>
This is the text version of the page
<%Else%>
This is the multimedia version of the page
<%End If%>

ASP Remove Session Variables
The Contents collection contains all session variables.

It is possible to remove a session variable with the Remove method.

The example below removes the session variable "sale" if the value of the session variable "age" is lower than 18:

<%
If Session.Contents("age")<18 then
Session.Contents.Remove("sale")
End If
%>

To remove all variables in a session, use the RemoveAll method:

<%
Session.Contents.RemoveAll()
%>

ASP Loop Through the Contents Collection
The Contents collection contains all session variables. You can loop through the Contents collection, to see what's stored in it:

<%
Session("username")="Mickey Mouse"
Session("age")=50dim i
For Each i in Session.Contents
Response.Write(i & "<br />")
Next
%>

Result:

username
age

If you do not know the number of items in the Contents collection, you can use the Count property:

<%
dim i
dim j
j=Session.Contents.Count
Response.Write("Session variables: " & j)
For i=1 to j
Response.Write(Session.Contents(i) & "<br />")
Next
%>

Result:

Session variables: 2
Mickey Mouse
50

Loop Through the StaticObjects Collection
You can loop through the StaticObjects collection, to see the values of all objects stored in the Session object:

<%
dim i
For Each i in Session.StaticObjects
Response.Write(i & "<br />")
Next
%>