1. Open Terminal (in /Applications/Utilities/)

2. Type the following:

sudo mdutil -E / to reindex the root volume
sudo mdutil -E /Volumes/volumename to reindex another volume named volumename.

3. Enter your admin password when prompted to do so and press enter.

4. You will receive the message �Volume index removed. Index will be rebuilt automatically.� in the Terminal window. You can monitor the reindexing progress in the Spotlight toolbar drop-down window.

5. Done

I say on portable mac's because if you have a desktop that never gets shut off, these run automatically.

sudo periodic daily weekly monthly