| Country: | AUT |
| Type: | A |
| Route: | 3 |
| Map: | Karte A3 AT.svg |
| Length Km: | 38 |
| Junction: | near Eisenstadt |
| Terminus B: | Eisenstadt border with |
| Regions: | Lower Austria, Burgenland |
| Cities: | Eisenstadt |
| Previous Type: | A |
| Previous Route: | 2 |
| Next Type: | A |
| Next Route: | 4 |
The Südost Autobahn (A3; 'Southeast Motorway') is a motorway, or ‘Autobahn’, in Austria. It runs from the Süd Autobahn at the junction Knoten Guntramsdorf southeast to Eisenstadt.
It was built between the 1970s and 1996, with multiple sections being opened for traffic once at a time.
Near Eisenstadt the A3 ends, where it crosses the Burgenland Expressway S 31 and merges into the B 16. Motorists can proceed on the B 16 towards the border with Hungary and enter the M85 expressway (Hungary) at Sopron. Plans to link the A3 and the M85 directly at the border have been abandoned by the Austrian authorities due to environmental and climate concerns.[1]