Recent studies suggest that phospholipids in the plasma membrane of mammalian cells are not homogenously distributed but may form domains either by lipid-lipid interactions or/and as consequence of lipid-protein interactions. Such lipid compartments may act as protein recruiting platforms which, for example, are essential components of cell signaling pathways. Model membrane systems with a defined lipid composition are ideally suited to study domain-specific interactions of peripheral and integral membrane proteins. Giant unilamellar vesicles (GUVs) offer the opportunity to directly visualize in parallel, both the lateral lipid domains and the interaction sites of proteins using fluorescence microscopy. The application of GUVs is exemplarly illustrated for studying domain-specific interactions of the protein alpha-synuclein and the domain-specific distribution of synthetic transmembrane peptides.