Warren Buffett- A three-pronged approach

From the Wikipedia entry on Buffett:
Buffett employed a three-pronged approach:

1. Generals: undervalued securities that possess margin of safety and meet expected return-to-risk characteristics ([8])
2. Arbitrages: company events that are not related to broader market changes, such as mergers and acquisitions, liquidation, etc.
3. Controls: build sizeable holdings, ally with other shareholders or employ proxies to effect changes in companies

In 1962 Buffett Partnerships began purchasing shares of Berkshire Hathaway, a large manufacturing company in the declining textile industry that was selling below its working capital. Buffett would eventually dissolve all his partnerships to focus on running Berkshire Hathaway. At the time, Charlie Munger, Berkshire's current Vice Chairman, remarked that purchasing the company was a mistake, due to the failure of the textile industry. Berkshire, however, became one of the largest holding companies in the world, as Buffett redirected the company's excess cash to acquire private businesses and stocks of public companies. At the core of his strategy were insurance companies, due to the large cash reserves ("float") they must keep on hand to pay out future claims. Essentially, the insurer does not own the float, but may invest it and keep any proceeds.

Under Munger's influence, Buffett's investment approach moved away from a strict adherence to Graham's principles, and he began to focus on high-quality businesses with enduring competitive advantages. He described such advantages as a "moat" that kept rivals at a safe distance, as opposed to commodity businesses, which sell undifferentiated products and face direct competition. A classic example of a wide-moat company is Coca-Cola, because consumers are willing to pay more for a Coke than for a generic beverage with a similar taste. On the other hand, salt is considered a commodity product because consumers generally have no preferences for one brand of salt over another.

Investment in wide-moat businesses has become a hallmark of Berkshire Hathaway, particularly when buying whole companies rather than public stocks. As a result, it now owns a large number of businesses which are dominant players in their respective industries, specialize in various niche markets, or possess other unique characteristics to separate them from their competitors.