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Stripe rust, caused by <i>Puccinia striiformis</i> f. sp. <i>tritici</i> (<i>Pst</i>), is a devastating fungal disease of wheat. The wild emmer gene, <i>Yr15</i> (<i>Wtk1</i>), which confers a strong broad-spectrum resistance to <i>Pst</i> isolates, is composed of kinase and pseudokinase domains. The analysis of 361 wild emmer accessions from a wide range of natural habitats confirms that functional <i>Wtk1</i> is distributed mainly along a narrow axis from Mt. Carmel to Mt. Hermon regions, in the northern part of Israel, where environmental conditions are favorable to the onset of stripe rust. An analysis of full-length <i>Wtk1</i> DNA sequences from 49 wild emmer accessions identified three haplotypes and extremely low nucleotide diversity (&#960; = 0.00002). The sequence diversity of <i>Wtk1</i> is 9.5 times lower than that of broad-spectrum partial resistance gene <i>Yr36</i> (&#960; = 0.00019), and both are in sharp contrast to the high level of nucleotide diversity previously reported for race-specific resistance genes (e.g., <i>Lr10</i> and <i>Pm3</i>). However, the nonfunctional <i>wtk1</i> sequences possess high level of nucleotide diversity (&#960; = 0.07). These results may reflect the different resistance mechanisms and the different evolutionary processes that shaped these resistance genes. <i>Yr15</i> was absent in 189 Chinese wheat landraces and was present in only 1.02% of the 583 tested modern Chinese wheat cultivars. These results corroborate our previous results showing that <i>Yr15</i> was absent in 94% of a worldwide collection of 513 wheat cultivars, therefore indicating the importance of <i>Yr15</i> in wheat stripe rust resistance breeding programs in China and elsewhere around the globe.