The first ISSI-Europlanet forum of the H2020 contract of Europlanet will gather 33 among the leading experts in Solar System planetary science, together with ten experts in space mission technologies, to reach the following objectives:

• Identify the outstanding open questions concerning our modern understanding of Solar System objects, their origin, formation and evolution, their processes and their system aspects, and their potential habitability;
• In association with this list of outstanding open questions, identify related representative ambitious space missions that could potentially address these questions over the coming 50 years, in preparation for the upcoming AAE-Cospar-Europlanet  Colloquium on “Planetary Exploration, Horizon 2061”;
• Address these objectives in the context of the rapidly-expanding science of exoplanets and their systems, which was the subject of the previous 2012 ISSI-Europlanet forum (Lammer et al., 2013);
• Propose a short list of Workshops addressing some of these outstanding science questions, with the aim of helping to make progress in the understanding of the science issues and in the elaboration of the corresponding representative space missions; these Workshops will be organized in the ISSI-Europlanet collaboration framework over the coming three years (2017-2019).

The expected outputs of this forum will be submitted to the November 2016 session of the Science Committee (SC) of ISSI, in order for ISSI and Europlanet to be ready to implement the proposed set of joint Workshops in the relevant timeframe.