South African franchises Toyota Cheetahs and the Southern Kings will join the Guinness PRO12 to create an enlarged tournament next season.
The tournament - which will be renamed the Guinness PRO14 Championship - will be split into two conferences of seven.
Each conference will be made up of two Welsh and two Irish teams, with one representative each from Scotland, Italy and South Africa.
The Pro12 has been expanded with South African teams Southern Kings and Toyota Cheetahs
'The agreement means that the Championship will take place across the northern and southern hemispheres and marks the first phase of expansion as the Guinness PRO14 becomes a truly global tournament,' Celtic Rugby and the South African Rugby Union said in a joint statement.
The groups have been based on last season's results with the Ospreys, Cardiff Blues, Munster, Connacht, Glasgow, Zebre and the Cheetahs in Conference A.
Last season's champions Scarlets, Dragons, Leinster, Ulster, Edinburgh, Benetton Treviso and the Southern Kings will line up in Conference B.
Teams will play each other home and away in their own section and sides out of their own conference once.
The 21-game season will be completed by