| Competition: | Regionalliga |
| Season: | 1965–66 |
| Winners: | FC St. PauliHertha BSC BerlinFortuna DüsseldorfFK PirmasensFC Schweinfurt 05 |
| Promoted: | Fortuna DüsseldorfRot-Weiß Essen |
| Relegated: | SV FriedrichsortVictoria HamburgSC TegelSC GatowViktoria 89 BerlinVfB BottropSTV Horst-EmscherSC LudwigshafenBSC OppauTSC ZweibrückenESV IngolstadtSpVgg WeidenVfR Pforzheim |
| Prevseason: | 1964–65 |
| Nextseason: | 1966–67 |
The 1965–66 Regionalliga was the third season of the Regionalliga, the second tier of the German football league system. The league operated in five regional divisions, Berlin, North, South, Southwest and West. The five league champions and four runners-up, the Regionalliga Berlin runners-up was not qualified, entered a promotion play-off to determine the two clubs to move up to the Bundesliga for the next season. The two promotion spots went to the Regionalliga West champions Fortuna Düsseldorf and runners-up Rot-Weiß Essen.
The 1965–66 season saw two new clubs in the league, Bremer SV and Itzehoer SV, both promoted from the Amateurliga, while no club had been relegated from the Bundesliga to the league.
The 1965–66 season saw seven new clubs in the league, 1. FC Neukölln, VfB Hermsdorf, Lichterfelder SU, SC Tegel, SC Gatow and SC Staaken, all promoted from the Amateurliga as the Regionalliga had been expanded from 10 to 16 clubs, while Hertha BSC Berlin had been relegated from the Bundesliga to the league.
The 1965–66 season saw two new clubs in the league, VfL Bochum and VfB Bottrop, both promoted from the Amateurliga, while no club had been relegated from the Bundesliga to the league.
The 1965–66 season saw one new club in the league, SV Alsenborn, promoted from the Amateurliga, while no club had been relegated from the Bundesliga to the league.
The 1965–66 season saw three new clubs in the league, Opel Rüsselsheim, VfR Pforzheim and SpVgg Weiden, all promoted from the Amateurliga, while no club had been relegated from the Bundesliga to the league.
The runners-up of the Regionalliga Nord and Regionalliga Südwest played a two-leg decider to determine which team qualified for the group stage, which 1. FC Saarbrücken won on aggregate.[1]
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