Generally, living trusts are established during an individuals lifetime and can be modified or changed while that person is still alive. Circumstances do change and the option to make alterations in the trust is important.
For this reason, a living trust is set up on a "revocable" basis. Revocable means you can modify or change the trusts provisions. Your other option would be to create an irrevocable trust. Once put in place, you are unable to change the terms of the trust regardless of the circumstances.
As you will see, living trusts speed up the process by which your property moves to your designated beneficiaries after you die. Today, and into the foreseeable future, this is vitally important as the United States is experiencing an unprecedented wealth transfer.