In recent years we have migrated a good number of sites from Plone 4 to 5, from Archetypes to Dexterity, from LinguaPlone to plone.app.multilingual and more recently from Python 2 to 3. Some migrations even combined all of the above. In this talk I will try to cover all the technical aspects of such large-scale migrations, will walk through many code-examples and discuss best-practices. All upgrade-steps and documentation will be provided for you to reuse.