The PAC-3 is the next-generation Patriot missile, employing hit-to-kill technology to intercept and destroy tactical ballistic missiles, cruise missiles and air breathing threats through direct body-to-body contact using a Boeing-built millimeter wave seeker.
For more information, read the Patriot Advanced Capability-3 (PAC-3) (PDF) overview.
If you do not have Adobe Acrobat Reader for reading PDF files, it is available for free from Adobe.