Emerging results suggest that the trigger of a variety of neurodegenerative diseases is the formation of pathogenic protein aggregates (“seeds”), which self-propagate in a prion-like manner. Current data support the hypothesis that progression of different neurodegenerative diseases can be caused by cell-to-cell spread of such proteinaceous seeds. We aim to elucidate the key mechanisms by which proteins misfold into toxic assemblies and then transfer between neurons and along neural pathways, thus facilitating the propagation of the disease in the CNS. By studying these mechanisms using a systematic approach at multi-levels from molecules, cells, organs to animal models and combining structural and biophysical techniques, biochemistry, cell biology, and imaging, we then aim to develop novel therapeutic targets to stop the self-replication and propagation and thus disease progression. To identify common molecular pathways we will mainly cross-examine two of these diseases, Alzheimer´s disease (AD) and Parkinson´s disease (PD), and concentrate on the analysis of amyloid-beta (Aß) and alpha-synuclein (aS) aggregates.