Llithfaen (Welsh pronunciation: [ˈɬɪθvaɨ̯n]) is a village on the North West of Wales on the Llŷn Peninsula in Gwynedd, Wales, in the historic county of Caernarfonshire. It is within the community of Pistyll.

There is a shop, pub, playground, community hall located in the village centre.

The population of Llithfaen was 821 in the 2021 census, with the population being 89% Welsh speakers.

There is a river called Afon Erch running from Llithfaen to the village of Abererch. The village of Trefor is nearby.

Pwllheli is the nearest town, approximately 9 miles (13 km) away and the town of Caernarfon is 16 miles (24 km) away Nant Gwrtheyrn is a Welsh Language Heritage Centre near the village. The nearest beach is Trefor Beach. Llithfaen is near Caernarfon Bay and the Irish Sea.

Llithfaen Calvinistic Methodist Chapel was built in 1780 and rebuilt several times to cope with the growing population. It was most recently rebuilt (Capel Isaf) in 1905.

In the first half of the 19th century, many smallholders of the parish supplemented their incomes by taking heather cut from the slopes of Tre'r Ceiri to be sold as kindling in Pwllheli for sixpence a bundle.

The population grew with the opening of granite quarries on Yr Eifl in the 19th century. Many houses were built, and the census in 1881 shows many immigrants from other areas of the peninsula, Penmaenmawr and as far as Scotland. Three quarries were close to the village, the last of which (Chwarel Carreg y Llam) closed in 1963. The other two were Y Nant and Caer Nant.

As of 2002, musician Ian Brown had a holiday home in the village.

The area is in the Senedd constituency of Dwyfor Meirionydd and the Westminster constituency of the same name.