This study evaluates the problematic notion of “reliability” with respect to Iryŏn’s (1206–1289) Samguk yusa (Memorabilia of the Three Kingdoms) and seeks to describe the extent to which this work is dependable as a vehicle for preserving anecdotes, legends, and lore from Korean antiquity. The Samguk yusa was not compiled for the purpose of preserving data to answer the types of questions modern historians ask; therefore, its validity and utility should not be judged by criteria it was never designed to fulfill. However, the extent to which it reliably reproduces the language of its sources can and should be measured to the extent that it is possible. This study examines four examples of Iryŏn’s borrowing from preexisting Chinese and Korean sources—by providing full translations and textual analysis—and demonstrates that the Samguk yusa, for the most part, reliably reproduces the language of its original sources. Although a strong editorial hand is visible, either that of Iryŏn or of a later individual, the evidence suggests that Iryŏn is consistent when citing preexisting sources and that Iryŏn’s editorial techniques conform to those practiced by his Chinese colleagues.