Baby showers are a relatively recent tradition, generally credited as having their start in the US. A baby shower is usually a relatively casual event, held in the afternoon or early evening, often with refreshments provided and sometimes party games held as well. It is not uncommon to have a potluck shower, where guests each bring a food item along with a gift, although fully catered showers are also quite common. Party games, if the host chooses to have them, generally center around the general theme of the baby and pregnancy, ranging from themed versions traditional games like charades to activities such as guessing the circumference of the pregnant guest-of-honor.
While many parents-to-be look forward to having a baby shower, some social groups feel such celebrations are best left as family affairs, or believe that it is bad luck to celebrate a birth before it happens. If you offer to host a shower for an expectant friend, don't be hurt if she politely declines. In other cases, the mother-to-be may have multiple showers! Perhaps one for co-workers and casual friends, and one for close friends and family. Some women have a baby shower only for their first child, while others may choose to have one for every pregnancy.
Baby showers are not bound by rigid traditions to the same extent as weddings and other life events, so don't be surprised if a new friend's baby shower is nothing like the last one you attended. There is really no "wrong" way to throw a baby shower, so if you have been charged with hosting a shower for a friend or relative, it's an "anything goes" affair (so long as you have the guest of honor's stamp of approval for your plans!).