Graham book, Security Analysis, with David Dodd, was published in 1934 and has been considered a bible for serious investors since it was written. It and The Intelligent Investor published in 1949 (4th revision, with Jason Zweig, 2003), are his two most widely acclaimed books. Warren Buffett describes The Intelligent Investor as "the best book on investing ever written."
Graham exhorted the stock market participant to first draw a fundamental distinction between investment and speculation. In Security Analysis, he proposed a clear definition of investment that was distinguished from speculations. It read, "An investment operation is one which, upon thorough analysis, promises safety of principal and a satisfactory return. Operations not meeting these requirements are speculative."
Graham wrote that the owner of equity stocks should regard them first and foremost as conferring part ownership of a business. With that perspective in mind, the stock owner should not be too concerned with erratic fluctuations in stock prices, since in the short term, the stock market behaves like a voting machine, but in the long term it acts like a weighing machine (i.e. its true value will in the long run be reflected in its stock price).
Graham recommended that investors spend time and effort to analyze the financial state of companies. When a company is available on the market at a price which is at a discount to its intrinsic value, a "margin of safety" exists, which makes it suitable for investment.
Graham wrote that investment is most intelligent when it is most businesslike, a statement which Warren Buffett regarded as the most important words about investment ever written. Graham said that the stock investor is neither right nor wrong because others agreed or disagreed with him; he is right because his facts and analysis are right.