The main objective of this paper is to review the criteria used to differentiate adults and immatures of Trumpeter and Tundra Swans with relevant emphasis on intraspecific variation. Field guides (e.g., Sibley 2014, Dunn and Alderfer 2017) provide detailed descriptions of Tundra and Trumpeter Swans, but they include limited information on the substantial intraspecific variation that occurs in both species. Several websites also compare the 2 swan species (e.g., Sibley 2006), but some of these sites consider only adults (McGowan and McGowan 2001, Madison Audubon Society 2021) even though immature birds can be more difficult to identify than adults. Despite progress in how field guides and websites illustrate and describe swan identification, differentiating Tundra and Trumpeter Swans can still present significant challenges.