Icahn is a director of Blockbuster Inc and the chairman of American Real Estate Partners LP, XO Communications Inc and American Railcar. Also he is a beneficial owner of Adventrx Pharmaceuticals Inc, Hollywood Entertainment, National Energy Group Inc, Vector Group Ltd and has significant holdings in Time Warner Inc. He has casino interests in Las Vegas, Nevada, including the Stratosphere, Arizona Charlie's Boulder and Arizona Charlie's Decatur, which are operated through American Entertainment Properties, a subsidiary of Icahn's major company American Real Estate Partners. Icahn has also tried to take over Marvel Comics.

In 2004, Icahn purchased a large bloc of stock in a pharmaceutical concern, Mylan Laboratories, after Mylan had announced a deal to acquire another company in that market, King Phamaceuticals, of Bristol, Tennessee. Icahn threatened a proxy fight over the acquisition, saying that the contract required Mylan to over-pay. He also contended that Mylan's chief executive, Robert J. Coury was significantly overcompensated and that Mylan's corporate governance was otherwise badly flawed.

In early 2005, Mylan gave up its efforts to acquire King, but management said this was a result of its ongoing monitoring of relevant facts, not due to pressure from Mr. Icahn.

Icahn Stadium on Randalls Island in New York City is named after him, as is the Icahn Science Center and Icahn Scholar Program at Choate Rosemary Hall, a top tier New England prep school.

Icahn made a substantial donation to his alma mater Princeton University (A.B., Philosophy, 1957) to fund a genomics laboratory which bears his name.

At the moment Icahn is also a major shareholder of Time Warner owning about 3.3% of the company valued at billions of dollars. He has been actively attempting to influence the direction of Time Warner, often in conflict with its Chief Executive, Richard Parsons. Although Time Warner recently sold 5% of its AOL division, Icahn has been pressing for additional action to increase shareholder value. On February 7, 2006, a group lead by Icahn and Lazard Frères CEO Bruce Wasserstein unveiled a 343-page proposal calling for the breakup of Time Warner into four companies and stock buybacks totaling approximately $20 billion. On February 17, 2006, the Icahn-lead group agreed with Time Warner to not contest the re-election of TW's slate of board members at the 2006 shareholders meeting. In exchange for the Icahn group's cooperation, Time Warner will buy back up $20 billion of stock, nominate more independent members to the board of directors, cut $1 billion of costs by 2007, and continue discussions with the Icahn group over their proposal, particularly on the future of Time Warner Cable.