Internal transcribed spacer (ITS nuclear rDNA) data have been obtained from 190 terrestrial orchid species, encompassing all genera and the great majority of the widely recognized species of Orchidinae, a heterogeneous selection of species of Habenariinae, and single species of Satyriinae and Disinae (the latter serving as outgroup). The resulting parsimony‐based phylogeny reveals 12 well‐resolved clades within the Orchidinae, based on Anacamptis s.l., Serapias, Ophrys, Steveniella–Himantoglossum s.l. (including ‘Comperia’ and ‘Barlia’, most species being 2n = 36), Neotinea s.l., Traunsteinera–Chamorchis, Orchis s.s., Pseudorchis–Amerorchis–Galearis–Neolindleya–Platanthera s.l. (most 2n = 42), Dactylorhiza s.l., Gymnadenia s.l. (most 2n = 40, 80), Ponerorchis s.l.–Hemipilia s.l.–Amitostigma–Neottianthe, and Brachycorythis (most 2n = 42). Relationships are less clearly resolved among these 12 clades, as are those within Habenariinae; the subtribe appears either weakly supported as monophyletic or as paraphyletic under maximum parsimony, and the species‐rich genus Habenaria is clearly highly polyphyletic. The triphyly of Orchis as previously delimited is confirmed, and the improved sampling allows further generic transfers to Anacamptis s.l. and Neotinea s.l. In addition, justifications are given for: (1) establishing Steveniella as the basally divergent member of an appreciably expanded Himantoglossum that incorporates the former genera ‘Barlia’ and ‘Comperia’, (2) reuniting ‘Piperia’ with a broadly defined Platanthera as section Piperia, necessitating ten new combinations, (3) broadening Ponerorchis to include Chusua, and Hemipilia to include single ‘orphan’ species of Ponerorchis and Habenaria, and (4) recognizing ‘Gymnadenia’camtschatica as the monotypic Neolindleya camtschatica within the Pseudorchis∼Platanthera clade. Few further generic transfers are likely in Orchidinae s.s., but they are anticipated among habenariid genera, on acquisition of additional morphological and molecular evidence; one probable outcome is expansion of Herminium. Species‐level relationships are also satisfactorily resolved within most of the major clades of Orchidinae, with the notable exceptions of Serapias, the derived sections of Ophrys, Himantoglossum s.s., some sections within Dactylorhiza, the former genus ‘Nigritella’ (now tentatively placed within Gymnadenia s.l.), Hemipilia s.l., and possibly Ponerorchis s.s. Relationships among the 12 major clades broadly accord with bona fide records of intergeneric hybridization. Current evidence supports the recently recognized 2n = 36 clade; it also indicates a 2n = 40 clade that is further diagnosed by digitate root‐tubers, and is derived relative to the recently recognized clade of exclusively Asian genera (Ponerorchis s.l.–Hemipilia s.l.–Amitostigma–Neottianthe). This in turn appears derived relative to the Afro‐Asiatic Brachycorythis group; together, these two clades identify the plesiomorphic chromosome number as 2n = 42. If the African genus Stenogolottis is correctly placed as b...