Ferret (Mustela putorius furo) and Mink (Neovison vison) CX3CL1 (C-X3-C motif chemokine ligand 1), also known as fractalkine, is a chemokine belonging to the CX3C chemokine family, characterized by three amino acids separating the first two conserved cysteine residues. In ferrets and mink, the CX3CL1 protein is identical at the amino acid level, indicating strong evolutionary conservation and suggesting similar biological functions in these mustelid species. CX3CL1 is unique among chemokines because it exists in both a membrane-bound form and a soluble form, allowing it to function in both leukocyte adhesion and chemotaxis. In these species, CX3CL1 is produced primarily by endothelial cells, epithelial cells, neurons, and macrophages in response to infection, inflammatory cytokines, or tissue injury. CX3CL1 binds to its receptor CX3CR1, which is expressed on monocytes, macrophages, natural killer (NK) cells, and subsets of T lymphocytes, promoting adhesion, migration, and activation of immune cells at sites of inflammation. Ferrets and mink are widely used as animal models for respiratory viral infections, including influenza viruses and SARS-CoV-2, where the CX3CL1–CX3CR1 signaling pathway contributes to immune cell recruitment to lung tissues and regulation of inflammatory responses during infection. Because these species show susceptibility and disease progression similar to humans for several respiratory viruses, characterization of CX3CL1 in ferrets and mink supports research on host–pathogen interactions, respiratory inflammation, and evaluation of antiviral therapies and vaccines.