The Neotropical spiders of the orbweaving genus Cyrtognatha Keyserling, 1881 (Tetragnathidae) are monographed. Cyrtognatha now includes a total of 21 species distributed over a large part of South America, Central America, and the southern parts of North America. Several species are known from the Caribbean islands of Cuba (one species), Hispaniola (two species), Jamaica (one species), and Saint Vincent (one species). Despite the wide geographic distribution of the genus, most Cyrtognatha species are known from single localities and often from very few museum specimens. The web architecture of several Cyrtognatha species is described and illustrated for the first time. Adults and juveniles of Cyrtognatha can be easily distinguished from all other tetragnathids by the presence of a straight line of long and robust macrosetae with enlarged bases on the retrolateral surface of the PLS. In Cyrtognatha the spermathecae are reduced and the sperm storage function is undertaken by an unpaired membranous structure, the posterior sac, which is diagnostic for the genus. A cladistic analysis including all known species of Cyrtognatha plus 51 outgroup taxa scored for a total of 194 morphological and behavioral characters was carried out. Thirteen unambiguous synapomorphies support the monophyly of Cyrtognatha, six of which are free of homoplasy. The internal phylogenetic relationships within the genus are also hypothesized and discussed. The genus Agriognatha O.P.-Cambridge, 1896 is a junior synonym of Cyrtognatha. The following eight new combinations are proposed: C. pachygnathoides (O.P.-Cambridge, 1894), C. bella (O.P.-Cambridge, 1896), C. lepida (O.P.-Cambridge, 1889), C. simoni (Bryant, 1940), C. rucilla (Bryant, 1945), C. espanola (Bryant, 1945), C. bryantae (Chickering, 1956), and C. insolita (Chickering, 1956). The following 11 new species are described: C. catia, n. sp., C. atopica, n. sp., C. eberhardi, n. sp., C. quichua, n. sp., C. waorani, n. sp., C. morona, n. sp., C. leviorum, n. sp., C. petila, n. sp., C. paradoxa, n. sp., C. orphana, n. sp., and C. pathetica, n. sp. The species C. aproducta Franganillo, 1926 is considered a nomen dubium. The follo