Mars planet-encircling or global dust storms are an iconic and enigmatic feature of the Red Planet. Occurring every few Mars Years, on average, they are a stochastic process in the otherwise largely repeatable annual cycle of martian weather. In 2018 (Mars Year 34 in the calendar of Clancy et al. [2000]), an international fleet of spacecraft, 6 orbiters and 2 rovers, observed the most recent global dust storm. This introduction and the articles of this special collection describe the evolution and impacts of the storm from the surface to the exosphere, compare this storm to previous global dust storms, identify new phenomena never-before seen in such storms, and attempt to determine how and when global dust storms develop.