Geotechnical engineering is an experience-driven discipline. Field observations are particularly important because it is difficult to replicate in the laboratory the characteristics and response of soil deposits built by nature over thousands of years. Furthermore, much of the data generated by a major disaster is perishable, so it is critical that it is collected soon after the event occurs. Detailed mapping and surveying of damaged and undamaged areas provides the data for the well-documented case histories that drive the development of many of the design procedures used by geotechnical engineers. Thus, documenting the key lessons learned from major extreme events around the world contributes significantly to advancing research and practice in geotechnical engineering. This is one of the primary objectives of the Geotechnical Extreme Events Reconnaissance (GEER) Association. Post-event reconnaissance and GEER are described in this paper, along with some of GEER’s findings from recent reconnaissance efforts. The use of advanced reconnaissance techniques is highlighted, as well as specific technical findings from the 1999 Kocaeli, Turkey earthquake, 2010 Haiti earthquake, 2010 Maule, Chile earthquake, 2010-2011 Canterbury earthquake sequence and 2014 floods that followed it, and the 2014 Oso, Washington landslide.