A MODEST review

We present an account of the state of the art in the fields explored bythe research community invested in "Modeling and Observing DEnse STellarsystems". For this purpose, we take as a basis the activities of theMODEST-17 conference, which was held at Charles University, Prague, inSeptember 2017. Reviewed topics include recent advances in fundamentalstellar dynamics, numerical methods for the solution of thegravitational N-body problem, formation and evolution of young and oldstar clusters and galactic nuclei, their elusive stellar populations,planetary systems, and exotic compact objects, with timely attention toblack holes of different classes of mass and their role as sources ofgravitational waves.Such a breadth of topics reflects the growing role played by collisionalstellar dynamics in numerous areas of modern astrophysics. Indeed, inthe next decade many revolutionary instruments will enable thederivation of positions and velocities of individual stars in the MilkyWay and its satellites, and will detect signals from a range ofastrophysical sources in different portions of the electromagnetic andgravitational spectrum, with an unprecedented sensitivity. On the onehand, this wealth of data will allow us to address a number oflong-standing open questions in star cluster studies; on the other hand,many unexpected properties of these systems will come to light,stimulating further progress of our understanding of their formation and evolution.