Aberllefenni is a village in the south of Gwynedd, Wales. It lies in the historic county of Merionethshire/Sir Feirionnydd, in the valley of the Afon Dulas.
It is the location of Foel Grochan, a slate quarry which together with Hen Chwarel and Ceunant Ddu formed the Aberllefenni Slate Quarry, which extracted rock from mediaeval times until the beginning of the 21st Century.
The Roman road between northern and southern Roman Wales, Sarn Helen, probably ran through the village; the terrace of houses known as Pensarn (head of the causeway) may be a reference to it.
Plas Aberllefenni (also known as "Y Plas") was a mediaeval manor house, but the older section was demolished in the 1960s and only a later wing is still standing.
The quarry reservoir, Llyn Cob, was once known as Llyn Owain Lawgoch, after the last male survivor of the princely house of the Kingdom of Gwynedd.
The quarry tips appear in the No Quarter: Jimmy Page and Robert Plant Unledded video when Jimmy Page and Robert Plant, formerly of Led Zeppelin, performed there with their band in August 1994.
The village is the site of a field study site for secondary school pupils.
Aberllefenni was the terminus of the narrow gauge Corris Railway, which carried slate from the quarries for transshipment at Machynlleth. Aberllefenni Station (now demolished) was used as the basis for Glennock Station on the fictional Skarloey Railway and can be seen illustrated in the book Four Little Engines.