CPPs are generally short cationic peptides that have the capability to interact directly with membranes. Most CPPs attain a three-dimensional structure when interacting with bilayers, while they are more or less unstructured in aqueous solution. To understand the relationship between structure and the effect that CPPs have on membranes, it is of great importance to investigate CPPs with atomic resolution in a suitable membrane model. Nuclear magnetic resonance (NMR) is an excellent technique both for studying solution structures of peptides as well as for investigating their location within a model bilayer. This chapter outlines protocols for producing model membrane systems for NMR investigations as well as the basic NMR tools for determining the three-dimensional structure of CPPs and for investigating the details in lipid-peptide interactions, i.e., the localization of the CPP in the bilayer.