It is difficult to determine the most popular nonfiction publications of all time as it depends on various factors such as the time period, geographical location, and the definition of popularity. However, some nonfiction books that have sold millions of copies and have had a significant cultural impact include:
"The Bible" - estimated to have sold over 5 billion copies
"Quotations from Chairman Mao Tse-Tung" (also known as "The Little Red Book") - estimated to have sold over 800 million copies
"The Diary of Anne Frank" - estimated to have sold over 30 million copies
"The Wealth of Nations" by Adam Smith - considered a classic in the field of economics
"The Origin of Species" by Charles Darwin - a seminal work in the field of biology and evolution
"The 7 Habits of Highly Effective People" by Stephen Covey - a popular self-help book.
It's worth noting that the above list is not exhaustive and there are many other nonfiction publications that have been popular over the years.