The main entry point to Baden-Württemberg by air is Stuttgart Airport (STR), located south of the city centre and connected to it by S-Bahn line S2 or S3 in about 27 minutes. Lufthansa, Eurowings, and several other European carriers serve Stuttgart. Fares from within Europe are often reasonable if booked ahead.
Freiburg has no commercial airport but sits close to Euro Airport Basel-Mulhouse-Freiburg (BSL/MLH/EAP), shared between Switzerland and France, which serves more routes than Stuttgart and is around 50 minutes by bus. Buses run direct from Freiburg main station. Karlsruhe/Baden-Baden Airport (FKB) is served mainly by Ryanair and handles a handful of European routes.
By rail, Baden-Württemberg is well integrated into the German and European ICE network. Stuttgart is a major hub: direct ICE trains connect it to Frankfurt (about 1 hour), Munich (about 2 hours 15 minutes), and Berlin (around 4 hours 30 minutes). Freiburg sits on the main Mannheim–Basel line and is 1 hour from Basel and about 2 hours from Zurich by IC.
If you're coming from France, Eurostar connections via Paris or direct TGV trains from Paris to Stuttgart (around 3 hours 15 minutes) make rail an attractive alternative to flying.
Driving into Baden-Württemberg is easy on the A8 (Munich–Stuttgart) and A5 (Frankfurt–Basel) autobahns. The German motorway network is generally excellent, though roadworks on the A8 around Stuttgart are a perennial frustration.