Prion diseases are infectious and fatal neurodegenerative disorders of man and animals which are characterized by spongiform degeneration in the central nervous system. In human diseases, the manifestation can be sporadic, familial or acquired by infection. Prion disorders are caused by the accumulation of an aberrantly folded isoform of the cellular prion protein (PrPc), commonly named PrPSc. Although prion diseases are usually rare, they have the potential to be transferred within and also between species by infection processes, giving then raise even to epidemic scenarios. As pathology is obviously restricted to the central nervous system pre-mortem diagnosis is usually hard to achieve. Promising approaches towards the development of therapeutic and even prophylactic anti-prion regimens were recently made. However, only a profound knowledge of the infectious agent and its replication strategy enables the design of effective anti-prion strategies. Cell culture models were highly instrumental in uncovering fundamental aspects of prion propagation. In this chapter, the cellular and molecular biology of prion proteins in general is discussed and prophylactic and therapeutic concepts derived thereof are introduced. In particular, emphasis is put on strategies targeting PrPc which is absolutely needed as substrate for prion conversion, and on intrinsic cellular clearance mechanisms for prions.