A taxonomic account is given of six Piper species of New Guinea: P. bolanicum spec. nov., P. gibbilimbum, P. recessum spec. nov., P. subbullatum, P. triangulare and P. wabagense. These small shrubby trees are best represented in secondary growth and forest at 1300–2500 m altitude, with P. gibbilimbum reaching c. 3000 m and P. bolanicum (and rarely P. triangulare) c. 3500 m. Piper subbullatum, the most widespread of the six in New Guinea, sometimes descends to sea-level there and is also found in the Philippines and from the Bismarck Archipelago to Vanuatu. The New World species P. aduncum and P. subpeltatum, adventive to New Guinea, are treated briefly. Piper recessum spec. nov. has been confused with P. gibbilimbum and P. subbullatum but is a completely glabrous plant. Its inflorescences have fleshy, asymmetrically peltate, strongly overlapping bracts. At anthesis the bracts move apart slightly; in the male the anthers dehisce underneath the bract-heads, while in the female the stigmas become (only just) visible between the sides of the bract-heads. One or more species of thrips may be this plant’s pollinators.