Many people decide to invest in gold by buying up stock in companies that mine gold. This can make money, but you need to know that when you do this, your success depends on a lot of other things besides the market price of gold going up.
It depends on the ability of the company management to produce gold at a competitive price. It also depends on their ability to get gold out of the land they own, and to acquire additional properties that turn out to have gold.
In short, it's a lot more complicated than today's closing price of gold in London. Gold producers are classified as: major companies, intermediates, and juniors.
The best responsible mining companies include Barrick Gold, Newmont Mining, AngloGold Ashanti, Gold Fields, Harmony Gold, Goldcorp, Freeport McMoRan Copper & Gold, Zijin Mining, Kinross Gold, Newcrest Mining, Buenaventura, OJSC Polyus Gold, and Rio Tinto.
These companies can be relied on to produce gold at a competitive price, and to not go out of business (unless bought out or merged, which happens). However, you may have to pay a high price for their name in the stock market. The Toronto Stock Exchange has the most gold companies listed. There are also a lot in New York, Vancouver, Johannesburg, London and Sydney exchanges.
Some companies mine gold but their main business is something else, such as Coeur d'Alene, which is primarily a silver producer.