The family Hylidae, as currently recognized, is composed of about 34 genera and more than 400 species. Most genera (30) and about 350 species live in the American tropics. _Hyla_ and 10 other genera inhabit Central America; four of those 10 genera (_Gastrotheca_, _Hemiphractus_, _Phrynohyas_, and _Phyllomedusa_) are widely distributed in South America. The other six genera are either restricted to Central America or have their greatest differentiation there. _Plectrohyla_ and _Ptychohyla_ inhabit streams in the highlands of southern Mexico and northern Central America; _Diaglena_ and _Triprion_ are casque-headed inhabitants of arid regions in Mexico and northern Central America. _Anotheca_ is a tree-hole breeder in cloud forests in Middle America. The genus _Smilisca_ is the most widespread geographically and diverse ecologically of the Central American genera. The definition of genera in the family Hylidae is difficult owing to the vast array of species, most of which are poorly known as regards their osteology, colors in life, and modes of life history. The genera _Diaglena_, _Triprion_, _Tetraprion_, _Osteocephalus_, _Trachycephalus_, _Aparasphenodon_, _Corythomantis_, _Hemiphractus_, _Pternohyla_, and _Anotheca_ have been recognized as distinct from one another and from the genus _Hyla_ on the basis of various modifications of dermal bones of the cranium. _Phyllomedusa_ is recognized on the basis of a vertical pupil and opposable thumb; _Plectrohyla_ is characterized by the presence of a bony prepollex and the absence of a quadratojugal. _Gastrotheca_ is distinguished from other hylids by the presence of a pouch in the back of females. A pair of lateral vocal sacs behind the angles of the jaws and the well-developed dermal glands were used by Duellman (1956) to distinguish _Phrynohyas_ from _Hyla_. He (1963a) cited the ventrolateral glands in breeding males as diagnostic of _Ptychohyla_. Some species groups within the vaguely defined genus _Hyla_ have equally distinctive characters. The _Hyla septentrionalis_ group is characterized by a casque-head, not much different from that in the genus _Osteocephalus_ (Trueb, MS). Males in the _Hyla maxima_ group have a protruding bony prepollex like that characteristically found in _Plectrohyla_. Ontogenetic development, osteology, breeding call, behavior, and ecology are important in the recognition of species. By utilizing the combination of many morphological and biological factors, the genus _Smilisca_ can be defined reasonably well as a natural, phyletic assemblage of species. Because the wealth of data pertaining to the morphology and biology of _Smilisca_ is lacking for most other tree frogs in Middle America it is not possible at present to compare _Smilisca_ with related groups in more than a general way.