According to this book, there are five different ways that people choose to express their affection towards each other (Physical Touch, Quality Time, Words of Affirmation, Acts of Service, Gift Receiving). You might not feel loved or cared for in a relationship if you and your partner have different languages of affection. This is equivalent to people speaking of the same things but not understanding each other due to a language barrier. Being aware of these differences can help you learn the love language of your partner. This book provides a useful tactical model for thinking about relationships, but I wouldn't call it an essential read.