A founder of the fields of behavioural ecology and neuroethology, Peter Marler’s research uncovered fundamental principles underlying how animals learn to communicate and employ signals in numerous contexts. Studying animal taxa as diverse as birds and primates, he helped illuminate how general principles underlie the communication of all animals. Further, he illustrated the power of comparative research to help us learn more about human behaviour and language. His approach shows us the importance of careful, curiosity-driven research inspired by natural history. Here, I discuss some of Peter Marler’s influential research findings and their impact on modern research in animal behaviour.