ABSTRACT: In many tropical animals, male and female breeding partners combine their songs to produce vocal duets. The temporal precision of these displays is often so astonishing that human listeners mistake duets for the songs of a single animal. Our understanding of vocal duetting behaviour is still rudimentary, in part because many duetting animals live in tropical habitats where dense vegetation makes direct behavioural observation difficult or impossible. Here I focus on the vocal duets of neotropical wrens using both descriptive and experimental approaches. In the first section of my talk I focus on the duetting behaviour of Rufous-and-white Wrens from the humid forests of Costa Rica. I use two innovative technical approaches to study vocal duets: an eight-microphone Acoustic Location System (ALS) capable of passively triangulating the position of duetting animals based on recordings of their vocalizations, and dual-speaker playback capable of simulating duets in a spatially realistic manner. Results from ALS recordings provide the first detailed spatial information on duetting animals, demonstrating that breeding partners perform duets across distances more variable than previously imagined and that duets play an important role in maintaining acoustic contact in visually occluded habitats. Results of dual-speaker playback demonstrate that duets play an important role in territory defense during aggressive confrontations with rivals, and that duetting birds use aggressive, sex-specific strategies for interacting with territorial intruders. In the second section of my talk I briefly describe the vocal duets of three related species of wren whose voices were unknown until recently: the Pacific Coast Plain Wren of Costa Rica, the critically endangered Niceforo's Wren of Colombia, and the recently described Inca Wren of Peru. My results support the argument that Neotropical wrens sing the most complex, coordinated songs ever described.