1. "The Night Watch" by Sergei Lukyanenko: This is a Russian fantasy novel that is the first book in the "Night Watch" series. The series is set in a world where magic is real and hidden from the ordinary people. It focuses on a group of "Watchers" who protect humanity from dark forces. It's highly popular in Russia and has been adapted into a movie.
2. "Night Watch" by Terry Pratchett: This is the title of a book in the "Discworld" series. While not a dedicated series of its own, "Night Watch" is a well-regarded book within the Discworld universe, focusing on the history of Ankh-Morpork's City Watch.
3. "The Watch" by Terry Pratchett: This is another potential point of confusion, as it is a sub-series within the Discworld series. While it doesn't have the "Night Watch" title, it includes many books focusing on the adventures of the City Watch, such as "Guards! Guards!", "Men at Arms", "Feet of Clay", and many others.
4. "Night Watch" by Tad Williams: This is the title of a short story included in the anthology "The Year's Best Fantasy and Horror". It's not part of a series.
To help me understand which series you're interested in, please tell me:
* What is the genre of the book series? (Fantasy, sci-fi, historical fiction, etc.)
* Do you remember any details about the plot or characters?
* Where did you hear about the series?
With more information, I can be more helpful in identifying the correct series.