SessionState Can be persisted in memory, which makes it a fast solution. Which means state cannot be shared in the Web Farm/Web Garden. Can be persisted in a Database, useful for Web Farms / Web Gardens. Is Cleared when the session dies - usually after 20min of inactivity. ViewState Is sent back and forth between the server and client, taking up bandwidth. Has no expiration date. Is useful in a Web Farm / Web Garden
SessionState
ViewState