Melanoma is a common cancer of dogs, especially those with significant amounts of skin pigmentation, but it is relatively rare in cats. The most common location for canine melanomas is the haired skin, where they grossly appear to be small brown to black masses, but they can also appear as large, flat, and/or wrinkled masses. Primary melanomas can also occur in the oral cavity, nailbed, footpad, eye, gastrointestinal tract, nasal cavity, anal sac, or mucocutaneous junction. Metastatic sites are numerous including lymph nodes (LNs), lungs, liver, meninges, and adrenal glands. This chapter will further review this complex set of melanocytic tumors in dogs and cats, with in-depth discussions on staging, diagnosis, prognostic factors, treatment options, and then some closing discussions on melanoma-based comparative and human oncology.