in case you weren't already aware, the 100 is a show based off of a book series of the same name, written by kass morgan. it's often debated in the fandom whether or not you "should" read them. all i have to say is: it's really not worth it.
the books are vastly different from the show. characters on the cw version do not exist in the novels, certain details are changed, etc. i read the first book and was so bored that i didn't even bother reading the last three of them and instead read spoiler-filled reviews on goodreads. the only reason why i might recommend reading them is if you're planning on writing a fanfiction. the books give much more detail into life on the colony (ark) than the show does.
MAJOR DIFFERENCES:
( in the least-spoilery way possible )
CHARACTERS
the only character from the show that exist in the books are clarke, wells, bellamy, octavia, and jaha. others such as jasper, monty, finn, raven, miller, harper, lincoln, lexa, etc are not present. there is also a character named glass who doesn't exist in the show. it can be assumed that she somewhat makes up raven's initial purpose in the series.
octavia is twelve at the start of the first book. the blake siblings' mother is named melinda and goes crazy while trying to keep octavia a secret, resulting in her trying to kill her daughter. bellamy walks in and stops it. melinda commits suicide with octavia in the same room. from then on, the two stay at a care center and octavia is not arrested for being a second child.
wells is not killed off for shock value.
bellamy and clarke are in a canon romantic relationship for the majority of the series. ("i want to spend eons with you, clarke griffin" SWOON)
both of clarke's parents were floated, not just jake.
the pilot episode has more action than the entirety of the first book.
there are other differences (obviously), but i can't reveal them without giving away major spoilers!
all-in-all, you can read the books for entertainment, but don't expect phenomenal writing and it to live up to the excitement of the show. the fact that it lacks a majority of fan-favorite characters really adds to the dryness and lackluster feel of the books. i skipped all of glass' chapters because they were that boring and found myself skimming most parts until i got to the end.