In this session, we'll walk you through the process of migrating your Drupal 7 website to D9, what are the stages of a migration project and how to plan thoroughly the implementation of a large migration. By the end of this session, you'll be ready to scope and prepare your upcoming migration and you'll know the key points for being able to scale your migration to hundreds of websites. We're going to share our recent experience of completing a large Drupal migration for the University of Waterloo (with more than 900 websites) and we'll share how we approached the project, the lessons learned, and some practical advice that will simplify your Drupal migration projects.This session is the result of a training webinar that we, at Evolving Web and Pantheon, presented together at the beginning of September and all the questions gathered from our audience there.