The aim of this study is a reinterpretation of the December 3, 1786, earthquake in the Outer Western Carpathians using known and newly found documents. The earthquake completed a set of events in the exceptionally active two-year period 1785–1786, when magnitudes and depths of epicenters reached, respectively, Mw = 5.3 and h = 35 km, being the strongest and deepest seismic events ever recorded in this region. Prior to the second half of the XVIII century, no earthquakes have been recognized; instrumentally, only 2 events, of Mw = 2.4 and Mw = 2.6, were recognized in the year 1994. Special searches were carried out in ecclesial and municipal archives to find unknown documents concerning the earthquake of December 3, 1786. New macroseismic maps have been compiled from qualitative data assessment of varying degrees of source significance and seismological importance. The mean parameters of the earthquake have been determined. High dispersion of intensity data points let us assume that it might have been not a single earthquake but a seismic swarm, with epicenters supposedly in the Upper Silesia, the Outer Western Carpathians, and the Inner Western Carpathians. The main earthquake in the years 1785–1786 occurred in the area of the Upper Silesian Block close to the tectonic junction of the Carpathian and Variscan orogenic fronts. References of the earthquake in manuscripts and contemporary journals, in the original languages as well as a catalogue of all localities where the quake was felt, including quotations translated into English, have been presented in a separate chapter at the end of this book.