The 4th International Workshop on Elastic Networks Design and Optimisation (ELASTICNETS 2017) is an open forum for discussion of research ideas related to Network Elasticity, QoS and optimisation.  The workshop is open, free (but requires registration) and does not aim to be a forum of publication. The workshop is funded by the Spanish Ministry of Economy and Competitivity (TEC2015-71932-REDT) and Telefonica.