The European Workshop on Software Ecosystems http://www.ewseco.org is an annual event which connects researchers and fellow professionals in the field of software ecosystems. Presentations in 2017 included: 1. Software M&A Ecosystems -- Industry Keynote by Julis Telaranta, Corum 2. Sandbox vs. Toolbox - Analyzing boundary Resource in B2B Software Platforms -- Maximilian Schreieck, Robert Finke, Manuel Wiesche, Helmut Krcmar 3. Manage multiple platform-ecosystems -- Christopher Jud, Georg Herzwurm 4. Survival of the smartest: Digitalization of mechanical engineering companies by creating a software ecosystem -- Industry Keynote by Benjamin Müller, ADAMOS GmbH 5. Building your IoT ecosystem: Proposing the Hybrid Intelligence Accelerator -- Dominik Dellermann, Nikolaus Lipusch, Philipp Ebel, Jan Marco Leimeister 6. The European Standard on eInvoicing EN16931 - Applications and Services to implement Directive 2014/55/EU on electronic invoicing -- Industry Keynote by Seeburger AG 7. Platform Business in Application Markets: Data Analytics of Mobile App Usage and Descriptions -- Lauri Frank 8. Fake it till you make it: how to bootstrap an ecosystem before your company is ready -- Alexander Eck, Benjamin Spottke 9. Strategy definition in large enterprise software ecosystems -- Ralf Meyer