A few years back I saw this book everywhere, but being young and scared I thought it was too adult for me. Once however I heard a speaker explain the theory in his lecture, and this year I've been taught it more in depth in the framework of my studies.
The theory is simple. Different things make different people feel loved. By learning the things that express love in a way that your partner (or anyone else in your life) understands, you discover the root of many conflicts and keep love alive in both of you.
The five languages of love are: Words of Affirmation, Quality Time, Receiving Gifts, Acts of Service, and Physical Touch.
What I liked about reading the actual book as opposed to having the idea presented to me in other ways was that through the examples and anecdotes the writer described I was able to identify the love languages of many other people besides my boyfriend- myself, my family and friends. You realize that at the heart of many cases of fallout there is a misunderstanding of what love is to the other person.
The book is short and quick read, approachable even if you've heard nothing about the theory. The writer is a Christian and expresses his beliefs throughout but it's nothing too serious or preachy at all. Recommended!