... by car:

from Germany on the A5 until exit
Weil am Rhein or the A 81 and various federal highways.
From Switzerland on the N 3 to the Basel toll and then the A 5 until exit Weil am Rhein. From France via Mulhouse (A36) or Strasbourg (A44)

... by train:

with IC / EC and ICE connections directly to Basel (Bad train station) and from there in a few minutes with regional trains to Weil am Rhein.

... by plane:

via Airport Basel-Mulhouse