This study investigates strategic intelligence failures of the pre-Vietnam and pre-9/11 time periods. The monograph presents PEMISI (political, economic, military, information, societal, and intelligence) environmental analyses of both time periods in order to evaluate whether intelligence lessons are truly similar in both periods. The intelligence observations presented are not an exhaustive representation of the U. S. Government's intelligence lessons from these two periods. Rather they are collected from comprehensive and quality studies of Vietnam and the 9/11 Commission Report and other sources. The resulting evidence suggests that five intelligence issues are similar between the two periods. A critical look at the similarities and disparities is made as a conclusion with the warning that contextual considerations are imperative for proper application of remedies. The monograph recommends historical education for analysts of intelligence pitfalls throughout history. Additionally, a caution is offered to policy-makers against the politicization of intelligence and need to understand and trust in the processes and professionals of the intelligence community.