The company is rolling out a $100m (£61.2m) plus global ad campaign and a new tagline 'Y!OU' created by WPP's Oglivy.
Yahoo! has not revealed how much it is spending in each market, but it is believed the company has committed £9m to the UK.
Other markets include the US, India, France, Brazil, Canada, Hong Kong, Indonesia, Korea and Taiwan.
Yahoo!'s redesigned homepage, which features a greater degree of personalisation and incorporates links to social networking sites such as Facebook, goes live today having been in beta for a short period.
The global campaign is focused on personalisation and how consumers can access multiple services and information online. It will run until the end of 2010.
The integrated activity is underpinned by a strong digital element that will kick off with a cross-platform campaign launching on October 5 in the UK.
TV ads, the company's first since 2002 when it ran a push for Yahoo! Finance, will run across Sky's network of channels.
The campaign also includes prints ads in a range of magazines and newspapers including Metro, The Guardian, GQ and Glamour.
As well as a digital outdoor campaign on the London Underground, Yahoo! will run online ads across its network, mobile sites and the homepage -- expandable banners will demonstrate how to take the "Y!OU" web experience on the go.
In addition, Yahoo! Search will include video ads and key products when people search for branded keywords on the search engine and Yahoo! Mobile will offers users ringtones featuring the Yahoo! Yodel for download.
The activity is being overseen by James Tipple, head of marketing for Europe, who joined in 2006 from Vodafone. He has also held senior marketing positions at BT Cellnet (O2) and GSK.