While the occurrence of landfill failures is rare, when they do occur the quantities involved can be huge. Ten large landfill failures are presented in this Lecture. Five are clay lined, and five are geosynthetically lined. Each failure was analyzed by 2-D and 3-D stability methods. It was found that 3-D analysis predicts higher FS-values in all cases; the average increase being 25%. It was also found that liquid was the trigerring mechanism in each failure case history. This was evidenced by (1) leachate buildup in the waste mass, (ii) wet clay beneath the geomembrane, and (iii) wet and soft foundation soil.