Between December 1951 and April 1967, Thomas R. Howell made 13 separate research trips to Nicaragua. The result was a collection of over 2,000 bird skins and at least 16 publications that form the backbone of Nicaraguan ornithology. In the late 1970s, Howell began working on a manuscript that was intended to be his major contribution to the ornithology of the country. The first version of this "Check-list of the Birds of Nicaragua" was not ready until 1983, and many different typewritten versions circulated among a small but growing number of Nicaraguan biologists for the next two decades. Partly because of Howell's passion for detail and completeness, and finally because of his failing health in the late 1990s, the check-list was never published before his death in December 2004. This monograph remedies what had become a significant obstacle to further studies in the country by providing, in Howell's own words, a comprehensive background for subsequent explorations. It documents the 654 species (611 supported with specimen evidence) known to have occurred in Nicaragua as of 1993, the date of the last substantial revision of the manuscript, and also provides a rationale for anticipating another 44 species. The publication of this significant chapter in the history of Central American bird studies is offered both as a tribute to Tom Howell's enthusiasm and contributions and as a frame of reference and springboard for current and future ornithologists inspired to study the rich and still largely unexplored avifauna of Nicaragua.