Eocene Baltic amber forms the largest amber deposit worldwide; however, its source vegetation and climateare much debated. Representatives of the oak family (Fagaceae) were abundant in the Baltic amber source areabased on numerous inclusions of staminate inflorescences or individual florets, previously assigned to Castanea andQuercus. However, the actual generic and infrageneric diversity of Fagaceae from Baltic amber remained unknown.Using flower characteristics and section-diagnostic in situ pollen of staminate inflorescences and detached floret inclusions,we describe 18 fossil-species of Fagaceae making this family by far the most diverse plant family preservedin Baltic amber. We substantiate the occurrence of the Castaneoideae, Quercoideae (Quercus sect. Cyclobalanopsis/ Lobatae; Q. sect. Lobatae; Q. sect. Protobalanus), Trigonobalanoideae and the extinct genus Eotrigonobalanus.Among the 18 fossil-species, six are described as new: Q. aimeeana, Q. casparyi, Q. multipilosa, E. campanulata,E. conwentzii, E. longianthera; and one new combination is published: Q. brachyandra (≡ Castanea brachyandra).In addition, a lectotype is designated for the name Quercites meyerianus and neotypes are designated for the namesCastanea inclusa and Quercus longistaminea (≡ C. longistaminea). Members of the Fagaceae probably inhabitedazonal and zonal vegetation types of the amber source area, including bottomland flood-plains and stream banks(Q. sect. Lobatae), dry habitats (Q. sect. Lobatae, Q. sect. Protobalanus), peaty soils, riparian and swamp forests(Castanopsis, Eotrigonobalanus), as well as mixed mesophytic forests (castaneoids, Quercoideae, trigonobalanoids).Affinities to extant North American and E to SE Asian floras support the recent notion that late Eocene Baltic amber(38 – 34 Ma) was formed in a warm-temperate climate.