What is love? How do we define it? Is love one thing or a set of many things? Are there different types of love? Is love the same for different types of relationships? Even as far back as the ancient Greeks, people have struggled with the nature of love. Poets have written about love perhaps as long as poets have been writing. Psychologists may lack the eloquence of poets, but through empirical research, we can study the nature of love systematically. We can observe people in different situations, interview them about their life experiences, and develop questionnaires to investigate people’s attitudes and behaviors. This way, definitions of love are drawn not only from personal opinion, but from scientific investigations.