The redesigned site will be opt-in on an initial basis, rolling out in the US today, and across Yahoo!'s international properties throughout the week.
Carol Bartz, chief executive, claimed the new homepage was Yahoo!'s most "radical" redesign yet. The company has rejigged its flagship website six times since it first hit the web in 1994.
It now features far fewer of Yahoo!'s own products and services, instead integrating with third-party websites -- often from rival companies -- saddled with display advertising.
Users can visit these third party sites without ever leaving the Yahoo! homepage and are served with targeted advertising whenever they do.
A prominent menu down the left hand side of the page allows users to customise the site through widgets, including links for third-party companies, such as Google's Gmail, or Twitter and MySpace.
Users can customise the Yahoo! News platform to include more "Fun" or "Serious" stories to suit their tastes.
Search queries can also be filtered just to include links from specific websites, such as eHow, YouTube, Amazon or Wikipedia.
The new homepage was originally slated for launch this fall, but the company surprised analysts with its early release.
Tapan Bhat, Yahoo! spokesman, said: "It's a sea change in the way we think about products, the way we think about users, and the way we think about our business."
The launch comes as Yahoo! continues negotiations with Microsoft about integrating their search and advertising products.
The deal, which has been rumoured for months, is understood to require Microsoft to pay Yahoo! $3bn upfront and then a share of its search advertising income.