The Nucleus (www.compadre.org/student) is the ComPADRE collection targeted at undergraduate students majoring in physics and astronomy.   It is assumed that undergraduates majoring in physics and astronomy might follow a wide array of career paths, so the types of resources included in the collection are correspondingly broad.  From its inception, the collection has had two primary goals:  Providing resources that will enhance the learning experiences of undergraduates, and providing tools and resources that will facilitate the establishment of an online community of physics and astronomy undergraduates.