A monthlong courtroom clash between Facebook Inc., Ireland’s data protection regulator, and Austrian privacy activist Maximilian Schrems is set to wrap up on Wednesday. The stakes are big for Facebook, but they are even bigger for the European Union’s digital economy. Depending on how the court rules, the legal mechanism that most companies rely on to transfer personal data outside the bloc—so-called Standard Contractual Clauses (SCCs)—could start to unravel.

Here’s an overview of how we got here: