CITES works by subjecting international trade in specimens of selected species to licensing controls. Species covered are listed in three appendices based on protection needs. Appendix I lists threatened species where trade is only allowed in exceptional circumstances. Appendix II includes species where trade must be controlled to avoid threats. Appendix III contains species a country requests help with trade controls. A CITES permit is required to import or export specimens, with different requirements based on the appendix the species is listed in. Exemptions exist for certain circumstances like personal effects or captive bred animals.