This talk highlights the issues that need to be addressed to successfully migrate from a GIS solution based on commercial products to a solution based on open-source software, in particular QGIS. What can be done? Where to start? What are the potential elements to convert? Which strategy to adopt? The talk will try to answer these questions by showing examples and lesson learned from successful Migrations. By presenting ad-hoc open source tools developed to solve specific problems and explaining how a migration can be tackled in cases where there are currently no specific tools we want to give you all the information needed to take informed decisions.