Home Depot (NYSE:HD) has been busy expanding the scope of its business. It announced yesterday that it is buying privately owned RMA Home Services, a company that specializes in the installation of replacement windows and siding.

If you're wondering what the big orange giant is up to, look no further than the firm's description of itself in its press releases:

Founded in 1978, The Home Depot is the world's largest home improvement specialty retailer and the second largest retailer in the United States, with fiscal 2002 sales of $58.2 billion. The company employs approximately 315,000 associates and has 1,644 stores in 50 states, the District of Columbia, Puerto Rico, eight Canadian provinces, and Mexico.

If you're already in all 50 states and raking in about $60 billion per year in sales, how do you keep growing? Sure, you can keep adding stores -- though at 1,644, you are probably already in most of the places you'd ideally want to be. You can also expand internationally, which the company has begun doing.

Another valid strategy is to broaden the scope of your business, as Home Depot and main rival Lowe's (NYSE:LOW) are doing. Instead of just selling roofing and flooring and windows and siding and appliances, you can sell installation services for roofing and flooring and windows and siding and appliances. This kind of expansion makes a lot of sense, as it's closely related to the Depot's core business and mission -- home improvement.

According to one report, Home Depot is enjoying sales growth of about 40% per year in its home installation services. Not too shabby! Learn more about Home Depot in this Dueling Fools battle from earlier this year and in this later one that pits Home Depot against Lowe's.

Also, pop in to our Home Depot and Lowe's discussion boards, where Fools like you are dissecting and discussing the companies. We're offering a free trial, so you might as well glean what you can.