© 2015 by the American Society of Plant Taxonomists. The suborder Jungermanniineae of the Jungermanniales is a major lineage of leafy liverworts, recognized in recent classifications to include 15 families. Gametophytes within the suborder are morphologically diverse, but commonly anisophyllous to distichous, usually with succubous, rarely transverse or incubuous, leaf insertions. Sporophytes are frequently, but not universally, enclosed by stemderived perigynia or coelocaules, often accompanied by perianth reduction or loss and some level of geocauly or marsupial development. We herein provide the first comprehensive molecular phylogeny of this geographically widespread suborder, using sequences generated from one nuclear (rpb2), two mitochondrial (nad1 and rps3), and seven plastid (atpB, psbA, psbT-H, rbcL, rps4, trnG and trnL) loci, sampled from 279 accessions representing 163 species in 57 genera. Ancestral states were reconstructed for 14 morphological characters generally considered taxonomically diagnostic for families in the suborder. Our phylogenetic analyses support the return of Leiomylia (=Mylia anomala) to the Myliaceae, removal of Myliaceae from the Jungermanniineae, and validation of the monogeneric suborder Myliineae subord. nov. to house it. Eighteen families are recognized within the Jungermanniineae, nine of which are monogeneric; namely, Endogemmataceae, Harpanthaceae, Gyrothyraceae, Arnelliaceae, Saccogynaceae, Geocalycaceae, Jackiellaceae, Notoscyphaceae stat. nov., and Trichotemnomaceae. The generic compositions of other families are modified as follows: Saccogynidium is transferred from Geocalycaceae to a newly named subfamily of Acrobolbaceae, Acrobolbaceae subf. Saccogynidioideae, and one other subfamily of the Acrobolbaceae is validated, Acrobolbaceae subf. Austrolophozioideae; Hygrobiella is included in Antheliaceae (previously in Cephaloziaceae or its own family); Jungermanniaceae is broadened to include Mesoptychiaceae and Delavayellaceae; Cryptocoleopsis and Nardia are transferred from Solenostomataceae to Gymnomitriaceae; Gottschelia, Herzogobryum, and Nothogymnomitrion are excluded from the Jungermanniineae; Solenostomataceae is recognized to include Solenostoma, Arctoscyphus, Cryptocolea, and Diplocolea. Additional nomenclatural changes include recognizing Horikawaella as a synonym of Solenostoma and Apomarsupella as a synonym of Gymnomitrion, establishing two new subgenera of Solenostoma, Solenostoma subg. Metasolenostoma and Solenostoma subg. Eucalyx, and transferring Jungermannia conchata to Cephalozia. Morphological character state reconstructions identify dioecious inflorescences, gametangia on leading stems, flagelliform or stoloniferous branches absent, dorsal leaf insertions not overlapping the stem midline, large underleaves, and lack of gemmae as ancestral within the Jungermanniineae. All morphological characters appear to be moderately to highly homoplasious within the suborder.