Eli Bendersky's website The secondary title of this book is "Thoughts on life and death at the brink of the millennium" which describes its contents pretty well. This is the last collection of articles and "thoughts" by Carl Sagan, and he died in 1996 (from some rare form of blood cancer) while putting the finishing touches to it.
After some short and delightful popular science notes, the bulk of the book is devoted to the difficult questions of how humanity should behave if it wants to survive for a long time. The most burning issues in this regard are of course preservation of the environment and demilitarization, especially getting rid of the tens of thousands of nuclear warheads in possession of the US and Russia.
It's not the best of Sagan's books, and is very similar to "The Pale Blue Dot" but as any of his books, it is far above average and well worth the effort to read.