This work presents results from the European Space Agency (ESA) space mission Gaia. Gaia data are being processed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC is provided by national institutions, in particular the institutions participating in the Gaia MultiLateral Agreement (MLA). The Gaia mission website is https://www.cosmos.esa.int/gaia. The Gaia archive website is https://archives.esac.esa.int/gaia. The Gaia mission and data processing have financially been supported by, in alphabetical order by country: – the Algerian Centre de Recherche en Astronomie, Astrophysique et Géophysique of Bouzareah Observatory; – the Austrian Fonds zur Förderung der wissenschaftlichen Forschung (FWF) Hertha Firnberg Programme through grants T359, P20046, and P23737; – the BELgian federal Science Policy Office (BELSPO) through various PROgramme de Développement d’Expériences scientifiques (PRODEX) grants and the Polish Academy of Sciences - Fonds Wetenschappelijk Onderzoek through grant VS.091.16N; – the Brazil-France exchange programmes Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) and Coordenação de Aperfeicoamento de Pessoal de Nível Superior (CAPES) - Comité Français d’Evaluation de la Coopération Universitaire et Scientifique avec le Brésil (COFECUB); – the Chilean Dirección de Gestión de la Investigación (DGI) at the University of Antofagasta and the Comité Mixto ESO-Chile; – the National Science Foundation of China (NSFC) through grants 11573054 and 11703065; – the Czech-Republic Ministry of Education, Youth, and Sports through grant LG 15010, the Czech Space Office through ESA PECS contract 98058, and Charles University Prague through grant PRIMUS/SCI/17; – the Danish Ministry of Science; – the Estonian Ministry of Education and Research through grant IUT40-1; – the European Commission’s Sixth Framework Programme through the European Leadership in Space Astrometry (ELSA) Marie Curie Research Training Network (MRTN-CT-2006-033481), through Marie Curie project PIOF-GA-2009-255267 (Space AsteroSeismology & RR Lyrae stars, SAS-RRL), and through a Marie Curie Transfer-of-Knowledge (ToK) fellowship (MTKD-CT-2004-014188); the European Commission’s Seventh Framework Programme through grant FP7-606740 (FP7-SPACE-2013-1) for the Gaia European Network for Improved data User Services (GENIUS) and through grant 264895 for the Gaia Research for European Astronomy Training (GREAT-ITN) network; – the European Research Council (ERC) through grants 320360 and 647208 and through the European Union’s Horizon 2020 research and innovation programme through grants 670519 (Mixing and Angular Momentum tranSport of massIvE stars – MAMSIE) and 687378 (Small Bodies: Near and Far); – the European Science Foundation (ESF), in the framework of the Gaia Research for European Astronomy Training Research Network Programme (GREAT-ESF); – the European Space Agency (ESA) in the framework of the Gaia project, through the Plan for European Cooperating States (PECS) programme through grants for Slovenia, through contracts C98090 and 4000106398/12/NL/KML for Hungary, and through contract 4000115263/15/NL/IB for Germany; – the European Union (EU) through a European Regional Development Fund (ERDF) for Galicia, Spain; – the Academy of Finland and the Magnus Ehrnrooth Foundation; – the French Centre National de la Recherche Scientifique (CNRS) through action “Défi MASTODONS”, the Centre National d’Etudes Spatiales (CNES), the L’Agence Nationale de la Recherche (ANR) “Investissements d’avenir” Initiatives D’EXcellence (IDEX) programme Paris Sciences et Lettres (PSL*) through grant ANR-10-IDEX-0001-02, the ANR “Défi de tous les savoirs” (DS10) programme through grant ANR-15-CE31-0007 for project “Modelling the Milky Way in the Gaia era” (MOD4Gaia), the Région Aquitaine, the Université de Bordeaux, and the Utinam Institute of the Université de Franche-Comté, supported by the Région de Franche-Comté and the Institut des Sciences de l’Univers (INSU); – the German Aerospace Agency (Deutsches Zentrum für Luft- und Raumfahrt e.V., DLR) through grants 50QG0501, 50QG0601, 50QG0602, 50QG0701, 50QG0901, 50QG1001, 50QG1101, 50QG1401, 50QG1402, 50QG1403, and 50QG1404 and the Centre for Information Services and High Performance Computing (ZIH) at the Technische Universität (TU) Dresden for generous allocations of computer time; – the Hungarian Academy of Sciences through the Lendület Programme LP2014-17 and the János Bolyai Research Scholarship (L. Molnár and E. Plachy) and the Hungarian National Research, Development, and Innovation Office through grants NKFIH K-115709, PD-116175, and PD-121203; – the Science Foundation Ireland (SFI) through a Royal Society - SFI University Research Fellowship (M. Fraser); – the Israel Science Foundation (ISF) through grant 848/16; – the Agenzia Spaziale Italiana (ASI) through contracts I/037/08/0, I/058/10/0, 2014-025-R.0, and 2014-025-R.1.2015 to the Italian Istituto Nazionale di Astrofisica (INAF), contract 2014-049-R.0/1/2 to INAF dedicated to the Space Science Data Centre (SSDC, formerly known as the ASI Sciece Data Centre, ASDC), and contracts I/008/10/0, 2013/030/I.0, 2013-030-I.0.1-2015, and 2016-17-I.0 to the Aerospace Logistics Technology Engineering Company (ALTEC S.p.A.), and INAF; – the Netherlands Organisation for Scientific Research (NWO) through grant NWO-M-614.061.414 and through a VICI grant (A. Helmi) and the Netherlands Research School for Astronomy (NOVA); – the PolishNational Science Centre through HARMONIA grant 2015/18/M/ST9/00544 and ETIUDA grants 2016/20/S/ST9/00162 and 2016/20/T/ST9/00170; – the Slovenian Research Agency through grant P1-0188; – the Spanish Ministry of Economy (MINECO/FEDER, UE) through grants ESP2014-55996-C2-1-R, ESP2014-55996-C2-2-R, ESP2016-80079-C2-1-R, and ESP2016-80079-C2-2-R, the Spanish Ministerio de Economía, Industria y Competitividad through grant AyA2014-55216, the Spanish Ministerio de Educación, Cultura y Deporte (MECD) through grant FPU16/03827, the Institute of Cosmos Sciences University of Barcelona (ICCUB, Unidad de Excelencia ’María de Maeztu’) through grant MDM-2014-0369, the Xunta de Galicia and the Centros Singulares de Investigación de Galicia for the period 2016-2019 through the Centro de Investigación en Tecnologías de la Información y las Comunicaciones (CITIC), the Red Española de Supercomputación (RES) computer resources at MareNostrum, and the Barcelona Supercomputing Centre - Centro Nacional de Supercomputación (BSC-CNS) through activities AECT-2016-1-0006, AECT-2016-2-0013, AECT-2016-3-0011, and AECT-2017-1-0020; – the Swedish National Space Board (SNSB/Rymdstyrelsen); – the Swiss State Secretariat for Education, Research, and Innovation through the ESA PRODEX programme, the Mesures d’Accompagnement, the Swiss Activités Nationales Complémentaires, and the Swiss National Science Foundation; – the United Kingdom Rutherford Appleton Laboratory, the United Kingdom Science and Technology Facilities Council (STFC) through grant ST/L006553/1, the United Kingdom Space Agency (UKSA) through grant ST/N000641/1 and ST/N001117/1, as well as a Particle Physics and Astronomy Research Council Grant PP/C503703/1. Our work was eased considerably by the use of the data handling and visualisation software TOPCAT, and STILTS Taylor (2005). This publication makes use of data products from NEOWISE, Wide-field Infrared Survey Explorer (WISE), a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. In addition to the currently active DPAC (and ESA science) authors of the peer-reviewed papers accompanying Gaia DR2, there are large numbers of former DPAC members who made significant contributions to the (preparations of the) data processing. Among those are, in alphabetical order: Christopher Agard, Juan José Aguado, Alexandra Alecu, Peter Allan, France Allard, Walter Allasia, Carlos Allende Prieto, Antonio Amorim, Kader Amsif, Guillem Anglada-Escudé, Sonia Antón, Vladan Arsenijevic, Rajesh Kumar Bachchan, Angelique Barbier, Mickael Batailler, Duncan Bates, Mathias Beck, Antonio Bello García, Vasily Belokurov, Philippe Bendjoya, Hans Bernstein†, Lionel Bigot, Albert Bijaoui, Françoise Billebaud, Nadejda Blagorodnova, Thierry Bloch, Klaas de Boer, Marco Bonfigli, Giuseppe Bono, François Bouchy, Steve Boudreault, Guy Boutonnet, Pascal Branet, Elme Breedt Lategan, Scott Brown, Pierre-Marie Brunet, Peter Bunclark†, Roberto Buonanno, Robert Butorafuchs, Joan Cambras, Heather Campbell, Christophe Carret, Manuel Carrillo, César Carrión, Fabien Chéreau, Jonathan Charnas, Ross Collins, Leonardo Corcione, Nick Cross, Jean-Charles Damery, Eric Darmigny, Peter De Cat, Céline Delle Luche, Markus Demleitner, Sékou Diakite, Carla Domingues, Sandra Dos Anjos, Laurent Douchy, Pierre Dubath, Yifat Dzigan, Sebastian Els, Wyn Evans, Guillaume Eynard Bontemps, Fernando de Felice, Agnès Fienga, Florin Fodor, Aidan Fries, Jan Fuchs, Flavio Fusi Pecci, Diego Fustes, Duncan Fyfe, Emilien Gaudin, Yoann Gérard, Anita Gómez, Ana González-Marcos, Andres Gúrpide, Eva Gallardo, Daniele Gardiol, Marwan Gebran, Nathalie Gerbier, Andreja Gomboc, Eva Grebel, Michel Grenon, Eric Grux, Pierre Guillout, Erik Høg, Gordon Hopkinson†, Albert Heyrovsky, Andrew Holland, Claude Huc, Jason Hunt, Brigitte Huynh, Giacinto Iannicola, Mike Irwin, Yago Isasi Parache, Thierry Jacq, Laurent Jean-Rigaud, Isabelle Jégouzo-Giroux, Asif Jan, Anne-Marie Janotto, François Jocteur-Monrozier, Paula Jofré, Anthony Jonckheere, Antoine Jorissen, Ralf Keil, Dae-Won Kim, Peter Klagyivik, Jens Knude, Oleg Kochukhov, Indrek Kolka, Janez Kos, Irina Kovalenko, Maria Kudryashova, Ilya Kull, Alex Kutka, Frédéric Lacoste-Seris, Valéry Lainey, Claudia Lavalley, David LeBouquin, Vassili Lemaitre, Thierry Levoir, Chao Liu, Davide Loreggia, Denise Lorenz, Ian MacDonald, Marc Madau