Ulwimi lwesiSwazi okanye isiSwati lulwimi lwesiNtu lweqela lesiNguni elithethwa eSwatini naseMzantsi Afrika ngamaSwati. Inani lezithethi liqikelelwa ukuba likwingingqi ye-2.4 yezigidi. Olu lwimi lufundiswa eSwatini nakwizikolo ezithile zaseMzantsi Afrika eMpumalanga, ngakumbi iindawo ezazisakuba yiKaNgwane. IsiSwati lulwimi olusemthethweni lwase-Eswatini (kunye nesiNgesi), kwaye sesinye seelwimi ezilishumi elinanye ezisemthethweni eMzantsi Afrika.
Igama elisemthethweni lithi "siSwati" phakathi kwezithethi zomthonyama; ngesiNgesi, isiZulu, isiNdebele okanye isiXhosa ingabizwa ngokuba yiSwazi. IsiSwati sihlobene kakhulu nezinye iilwimi zesiTekela, njengesiPhuthi kunye noMntla weTransvaal (iSumayela) Ndebele, kodwa sikwasondelelene kakhulu neelwimi zesiZunda: isiZulu, isiNdebele saseMzantsi, isiNdebele saseMntla, nesiXhosa.