What are the major factors that determine the value of a firm's stock?

Answer

The price of a firm's stock is determined by the market - what are people willing to pay for it. You might consider things like Net Book Value and Price/Earning ratio; but you also have to consider other business conditions: Has the company just secured a valuable patent or trademark that has not produced any income yet? Are they suceptible to other market trends (good or bad) such as mortgage companies feeling the impact of a declining real estate market. And don't ever confuse a good product with a good company - a poorly managed company will fail regardless of their products.

A stock is considered over valued if the combined market price of all the company's shares is above the expected future value of the company, and it is considered undervalued if the combined market price of all the company's shares is below the expected future value of the company.