Ground-based mid-infrared astronomy is at a major turning point. Subaru/COMICS, which is one of the longest-serving and therefore probably the most heavily used mid-infrared instruments in the world, will be decommissioned as of the semester S20B. On the other hand, a new mid-infrared instrument MIMIZUKU developed for the 6.5-m TAO telescope will start its science operation around 2021. The next flagship mid-infrared instrument MICHI for TMT is also firmly taking shape. This workshop“Mid-infrared Astronomy ?Past 20 years and Future 20 years” is designed to summarize achievements and lessons learned in the 20-year history of Subaru/COMICS, to refine further the science cases for MIMIZUKU and MICHI, and to discuss future directions for the ground-based mid-infrared astronomy in the next 20 years.