''The PortletSession interface provides a way to identify a user across more than one request and to store transient information about that user.''

''A PortletSession is created per user client per portlet application.''

''A portlet can bind an object attribute into a PortletSession by name. 

* The PortletSession interface defines two scopes for storing objects:''
** APPLICATION_SCOPE
** PORTLET_SCOPE

''All objects stored in the session using the APPLICATION_SCOPE must be available to all the portlets, servlets and JSPs that belongs to the same portlet application and that handles a request identified as being a part of the same session.''

''Objects stored in the session using the PORTLET_SCOPE must be available to the portlet during requests for the same portlet window that the objects where stored from. Attributes stored in the PORTLET_SCOPE are not protected from other web components of the portlet application.''

''They are just conveniently namespaced. The portlet session is based on the HttpSession. Therefore all HttpSession listeners do apply to the portlet session and attributes set in the portlet session are visible in the HttpSession and vice versa.''

Pasted From http://www.bluesunrise.com/portlet-api/javax/portlet/PortletSession.html( BrokenLink )