The book actually follows two characters whose lives are loosely connected. The titular character, Anna Karenina, is married to a statesman, Alexei Karenin, and they have a young son, Seryozha. She has everything she could possibly want -- or so she thinks until she meets the young, dashing Count Vronsky.
The second storyline follows Konstantin Levin, whom Tolstoy based largely on himself. Levin wants nothing more than a simple country living and a family to share it with, but the girl he loves, Kitty, has refused him because Vronsky has been flirting with her.