The Internet has been matchmaker to thousands of now-married or dating couples. Even if you're not in the market for a spouse, you might welcome a dinner companion or even an online flirtation. Dating sites have become especially popular among singles in their 40s and 50s because they offer a grown-up alternative to the bar scene.

Online dating sites use the same technology that computerized dating services did in the 1960s. After you answer a series of questions to create a profile, most sites then compare the qualities you describe in yourself to those you're looking for in a man and find matches. If you'd rather make your own match, you can search the profiles according to various categories (age, physical attributes, location, education, likes, dislikes) and view the profiles yourself.

Most dating sites ask subscribers standard questions about height, weight, body type, smoking and drinking habits, education and location. Some may want you to list recently read books, favorite musicians or songs, the five things you can't live without, the kind of person you're looking for or what you have to offer. Each site is different, but all want to gather as much information as possible to paint a detailed picture of who you are and what you're looking for.

While some online dating services are free, the majority charge fees, which usually cover a period of time or a maximum number of contacts. Most sites allow a free trial or limited use before requiring payment, and each site has its own personality. So it makes sense to take a sneak peek before committing yourself financially. Many dating sites are geared to specific identities based on age, religion, race or sexual preference. Jdate.com, for example, is the leading Jewish singles networking site, Gay.com caters to gays and lesbians and Seniorfriendfinder.com targets seniors. And some sites are racier than others: For instance, Nerve.com is younger and more "out there" than Match .com or Eharmony.com.

You should definitely post a picture: Statistics show that profiles with a photograph are viewed more often than those without one. Stick with one that reveals the true you. Posting a 20-years-younger or 20-pounds-lighter shot only misleads any potential match and ends up doing a disservice to both of you. (As for uploading the photo onto the site, your digital camera should come with a USB cable and instructions on how to get your photos onto your hard drive; if you have a nondigital camera, ask your photo processor to put the developed photos on a CD. From there, the dating site itself should have instructions for posting the photo.)

If you find a profile that interests you, there are usually two routes available: You can e-mail the person through an anonymous e-mail account set up through the site, or you can send a "wink"-an unwritten message that brings your profile to the person's attention so he can decide whether to make contact. You have no obligation to respond to anyone who contacts you, nor should you be hurt if you don't hear back from someone you've contacted. You may not be his type, or perhaps he has already found someone and neglected to take down the profile. If you prefer to be the date seeker and not have others window-shop your profile, you can make it private, choosing whether and when to reveal it.

Online dating requires all the usual cautions, and then some. Never divulge your last name or home address before meeting a person face-to-face. If you choose to talk by telephone, give a cell phone number so no one can trace your home address. For a first meeting, keep it brief (a cup of coffee is good) and in a public place. As an extra precaution, make sure a friend or family member knows what you're doing, when and where. Under no circumstances should you get into a car with the person or meet in an isolated area.