The professional practice of civil engineering has long benefitted and advanced as the result of lessons learned from failures of both engineered and non-engineered structures. This monograph provides a comprehensive summary of lessons learned from both failures and sub-failures ('near misses' or 'close calls') in geotechnical and foundation engineering and related structural engineering, what the author refers to collectively as geo-structures and geo-structural systems. This presentation is based on the author's more than 50 years of professional experience as a civil engineer specializing in geotechnical and foundation engineering. This monograph also contains the author's observations on the professional practice/business aspects of forensic engineering as applied to geo-structures. This monograph is intended to be a resource document for both experienced and entry-level civil engineers who want to learn more about the professional practice of forensic engineering as applied to geo-structures which is distinctly different from other practice areas of civil engineering such as design, construction, and academia.