Instinctive behaviours, such as hunting, pup care and defence have evolved to ensure survival without the need for learning. In vertebrates, instinctive behaviours are generated by remarkably conserved brain circuits, and it has become increasingly clear in recent years that instinctive behaviours are flexible in regard to both action selection and execution. Despite a large body of behavioural work, the neural mechanisms underlying the flexible implementation of instinctive behaviours remain largely unknown. In this talk, I will discuss how excitatory and inhibitory neural circuits in the midbrain periaqueductal gray shape the initiation and execution of instinctive behaviours, and how they may support action selection during motivational conflict.