Berscheid and Hatfield (Berscheid & Walster, 1974; Hatfield, 1988; Walster & Walster, 1978) were the first to articulate a clear theoretical distinction between passionate love and companionate love. Passionate love can be characterised as an intense state of longing for another. It is associated with both positive states, such as elation and excitement, and with negative states, including pain and anxiety. Berscheid and Hatfield also proposed a formal theory of passionate love. This theoretical model posits that passionate love includes 1) a physiological component requiring intense arousal and 2) a cognitive process in which contextual cues suggest that ‘passionate love’ is an appropriate label for their feelings. Companionate love is a less intense state involving friendship, understanding, and concern for others’ welfare. It includes elements of intimacy, respect, trust, liking, and balance of power between partners. We describe how each of these types of love are assessed and their importance to the broader relationships literature.