Very informal, just one round phone interview. It was very to the point, clear cut interview questions (since this internship is targeted at college students and recent graduates). You can tell the staff is incredibly passionate about what they do. I interviewed with the Chicago branch (826CHI) and the woman I talked to was extremely friendly. At the end they try to gauge your creativity and fit for the organization by giving you a two minute "homework assignment." Mine was to, in two minutes, write a brief story about a alligator, camel, and a gallon of milk.