Greek life at Duke is pretty big; not as huge as, say, the basketball following, but huge nonetheless. You can survive socially without being a member, but you won’t get through Duke without being at least somewhat affected by Duke’s Greek scene. The number of students in fraternities or sororities might be a bit overwhelming at first, but it’s easy to understand after a bit. There are several Greek groups that don't fit the stereotypical mold of meathead jocks and perfect, pearl-wearing girls; instead, they are just groups of casual friends with social lives scheduled by the Greek chapter. It is not imperative to be Greek in order to have a healthy social life, but it certainly doesn't hurt. Greeks may be a minority within the entire student body, but the majority of the social scene is definitely controlled by Greeks, so most students will at least investigate their options by participating in rush in the spring.
Don’t be discouraged if you don’t feel like joining some selective living group. It is quite possible to thrive at Duke without going Greek. However, you’ll want to take Greek life into account when you’re choosing a college. The cliques and groups can be irritating at times throughout the year, but other than a few bad apples, the Greeks at Duke are quite open and friendly.