The rapid ongoing changes in software and hardware put digital information at risk. The challenge is to keep electronic data accessible, viewable, and usable for the future when the original software to interpret them has become unavailable. Digital preservation has thus turned into on of the most pressing challenges not only within the digital library community, but also in other areas such as archives and data centres. This chapter introduces the concepts and challenges in the field of digital preservation including the OAIS reference model. We give an overview about the projects and initiatives worldwide dealing with this challenge. We furthermore present preservation planning as a key concept at the heart of preservation endeavours in detail.