Yahoo and Microsoft have unveiled a tie-up that they hope will enable the two firms to better compete with Google in the internet search marketplace.
Microsoft's search engine will now power the Yahoo website, while Yahoo will in turn become the advertising sales team for Microsoft's online offering.
Here we take a closer look at the three US corporate giants.
Yahoo is the world's second most popular internet search engine, yet it trails far behind market leader Google.
Yahoo rejected a takeover bid from Microsoft last year
According to recent industry figures, Google has more than 64% of the search market in the US, while Yahoo has 20%.
Yahoo revealed last week that its revenues for the quarter to 30 June fell 13% to $1.57bn (£953m), blaming the challenging economic environment.
Profit for the quarter edged up to $141m from $131m.
Last year Yahoo rejected a $47.5bn or $33 per share takeover bid from Microsoft, an offer that was eventually withdrawn in May 2008.
Yahoo's shares are now worth around $17.
Founded in 1995, Yahoo is based in Sunnyvale, California.
It currently employs 14,300 staff.
Google was set up in 1998 by Larry Page and Sergey Brin, who had met at Stanford University, and is now the world's most used search engine.
Google remains by far the leader of the search engine market
Its shares were listed on Wall Street at a price of $85 in August 2004 and now trade at about $440 a share.
Earlier this month it reported a net income of $1.48bn for the three months to 30 June, compared with $1.25bn a year before.
Revenue rose 3% for the period at $5.52bn, and just over half - 53% - came from outside the US.
It has more than 17,000 employees in 20 countries and its headquarters, the Googleplex, are in Mountain View, California.
Microsoft dominates the world of personal computer operating systems, with a market share of about 90%.
Microsoft has made Bill Gates a very wealthy man
Despite this strength, it has remained relatively weak in the search engine market, with just an 8% stake in the US.
To help increase this, Microsoft revamped and renamed its search engine in May, which is now called Bing.
Earlier this week, the firm announced that its profits for the April to June quarter were down by almost a third from a year earlier, due to weaker global computer sales.
Founded in 1975, Microsoft enjoys annual revenues of $51bn and has a workforce of 79,000.
Headquartered in Washington State, co-founder Bill Gates is one of the world's richest men, with an estimated personal fortune of $56bn.
The company's dominant market position has led to numerous criticisms that it stifles competition.
Last year, the EU fined Microsoft 899m euros ($1.4bn; £680.9m) for abusing its market position after the US firm lost its appeal.
In February of this year, the European Commission launched two new anti-competition investigations into the company.