The chapter explains how the bodies, nervous systems, and brains of animals and humans evolved, developing their abilities to love. It also describes how the peripheral and central nervous systems evolved to enable mammalian and human love. The author presents a systematic review of multiple research findings demonstrating how various chemical messengers of love and their pathways work in the body and brain to produce love-related experiences and behaviors. In particular, the chapter describes how various brain regions and their systems, neurotransmitters, peptides, hormones, and somatic and autonomic nervous systems are involved in producing different types of love experiences, such as sexual love, romantic love, passionate love, maternal love, and infant attachment.