The 157 species of dynastine scarab beetles that occur in Costa Rica and Panama are comprehensively reviewed. Keys, descriptions, distributions, and notes on biology are provided for all species as well as illustrations and maps. The larvae of Enema endymion, Heterogomphus chevrolati, and Dynastes hercules are described for the first time. Also included are synopses of the higher-level taxa, a glossary, a gazetteer of place names, and a species checklist. The following new species are described: Cyclocephala alazona, C. enigma, C. labidion, C. marylizae, C. mustacha, C. stockwelli, C. unamas (all Cyclocephalini); Irazua dilicra (Oryctini); Amblyoproctus centroamericanus, Hemiphileurus curoei, H. dyscritus, H. nebulohylaeus, H. pygidiopunctissimus (all Phileurini); Golofa hirsuta and G. solisi (Dynastini). Irazua is described as a new genus of Oryctini. The following new synonyms are recognized: Cyclocephala dissimulata Ratcliffe (= C. almitana Dechambre), C. howdeni Endrodi (= C. carbonaria Arrow), C. obscurata Endrodi (= C. castaniella Bates), C. conspicua gregaroides Dechambre and C. conspicua fusca Dechambre (= C. conspicua Sharp), C. mollis Endrodi (= C. epistomalis Bates), C. barroensis Endrodi (= C. herteli Endrodi), C. rorschachoides Ratcliffe (= C. krombeini Endrodi), C. pseudisabellina Endrodi (= C. mutata Harold), C. vitracelis Dechambre (= C. mutata Harold), Stenocrates difficilis Endrodi (= S. bicarinatus Robinson) (Cyclocephalini); Hemiphileurus variolosus striatus Endrodi (= H. variolosus (Burmeister)) (Phileurini); and Aegopsis westwoodi Thomson (= A. curvicornis Burmeister) (Agaocephalini). The following names reflect a change in status because all are resurrected from synonymy: Cyclocephala brevis Hohne, C. multiplex Casey, C. mutata Harold, and C. ovulum Bates (Cyclocephalini).The following names are combinations resulting from a change in genus from Ligyrus to Tomarus: Tomarus bituberculatus (Palisot de Beauvois), T. cicatricosus (Prell), T. ebenus (DeGeer), T. fossor (Latreille), T. gyas Erichson, T. laevicollis (Bates), T. maternus (Prell), T. nasutus (Burmeister), T. sallaei (Bates), and T. similis (Endrodi). Lectotype and paralectotype designations are made for the syntypes of Hemiphileurus cylindroides (Bates). The generic name Enema is designated a nomen protectum, and the generic name Hoplites is designated a nomen oblitum. The following Cyclocephalini are reported for the first time from Costa Rica: Ancognatha atacazo Kirsch, A. vexans Ratcliffe, Aspidolea kuntzeni Hohne, A. notaticollis Hohne, C. erotylina Arrow, C. fasciolata Bates, C. ligyrina Bates, C. prolongata Arrow, Erioscelis columbica Endrodi, Stenocrates bicarinatus Robinson, S. hardyi Dechambre, and S. laevicollis Kirsch. The following Cyclocephalini are reported for the first time from Panama: Cyclocephala epistomalis Bates and C. rogezi Dechambre. The following species have been reported from Costa Rica and/or Panama, but since they have never been collected since being reported, or they are so far out of their normal range, I consider the records to be erroneous, spurious, or otherwise suspect: Cyclocephala cartwrighti Endrodi, C. freudi Endrodi, C. gregaria Heyne and Taschenberg, C. laminata Burmeister, C. lurida coahuilae Bates, C. obesa Burmeister, C. simulatrix Hohne, C. tutilina Burmeister, and C. warneri Ratcliffe. The following Pentodontini are reported for the first time from Costa Rica: Euetheola bidentata Burmeister, Tomarus cicatricosus (Prell), T. laevicollis (Bates), and T. maternus (Prell). The following Oryctini are reported for the first time from Costa Rica: Enema pan (Fabr.) and Xyloryctes splendidus Prell. The following Phileurini are reported for the first time from Costa Rica: Amblyodus taurus Westwood and Hemiphileurus dejeani (Bates). The following Agaocephalini are reported for the first time from Costa Rica: Aegopsis curvicornis Burmeister and Spodistes beltianus (Bates).