CSS (the Content Scrambling System)
This uses data encryption techniques to scramble video on the DVD media, preventing playback on DVD devices that don't have the decryption capability, and is 100% effective in preventing Digital-to-Digital copying on PCs. CSS protected discs can also be region coded to play in one or more of 6 specific world regions.

ACP (the Analog Copy Protection system from Macrovision)
This is implemented as two control bits in the MPEG-2 video stream. The bits are set during the authoring process to switch on ACP in DVD players. ACP is 100% effective in preventing DVD Recorder copying, as well as copying to VCR recorders etc.