The two announced their plans on a video blog.
After gaining fame in the '90s and early 2000s with hits like "The Rain," "Sock It to Me" and "Get Ur Freak On," the two ceased working together following the release of Elliott's 2005 album, The Cookbook.
In intervening years, Elliott has largely faded from the public spotlight, while Timbaland has turned his attention toward pop albums by Justin Timberlake, Nelly Furtado, Ashley Simpson, Chris Cornell and Madonna.
"We're back. We're here. We ain't goin' nowhere," said Elliot, who thanked fans on Twitter and Facebook for showing her support. "When you've been in the game 18 years, it's not called 'washed up,' it's called 'iconic.' It's called 'legends,'" she said.
Download Timbo and Missy's latest collaboration, a release from the "Timbaland Thursdays" series, here. Timbaland says they're shooting a video for the track, and that they're working on Elliott's long-anticipated seventh album, Block Party, as well.