Auditory callback is the standard method for monitoring rails and other secretive marsh birds that live in concealing habitats. Due to recent population declines, monitoring the King Rail (Rallus elegans) has become a conservation priority. Analysis of field recordings (n = 542 calls or notes) and behavioral observations were combined to provide an account of the structure and function of the King Rail's vocal repertoire, which included 10 different vocalizations. King Rails produced an array of pulsed sounds by altering frequency, note length, pulse rate, and amplitude of each call. The most commonly heard call, the grunt (61 calls recorded; 37 individuals), had multiple functions including mate communication, duetting, and interaction with neighbors in a ‘roll call’ context. The kek (208 calls; 46 individuals) was the primary mate advertisement call. Most of King Rail's calls, including alarms (165 notes; 7 individuals), screeches (47 calls; 7 individuals), churrs (43 calls; 10 individuals), and the poorly documented boom (5 calls; 5 individuals), were used and sometimes combined in defense and distress situations. Although previously described as a signal of receptivity by females, the kek-burr may also be used in the context of defense. This synthesis is intended to assist researchers and managers in interpreting behavioral observations and improving effectiveness of audio lures for detecting or trapping King Rails.