Fluorescent labeled peptides, peptides with a reporter fluorescent dye, are valuable probes used in visualizing intracellular processes and molecular interactions at the level of single cells. The fluorescent dye can be attached to the amino (N) or carboxy (C)-terminus, or in the case of FRET (Fluorescence or Forster resonance energy transfer) peptides, the two dyes (donor and acceptor) can be at the amino and carboxy termini or in the internal peptide sequence. Fluorescent labeled peptides are powerful tools for the investigation of biological relevant interactions such as receptor-ligand binding, protein structures, and enzyme activities.