Tudweiliog is a small, predominantly Welsh-speaking village and community on the northern coast of the Llŷn Peninsula in the Welsh county of Gwynedd.

The village name was often spelt "Tydweiliog" until the 1980s, representing a local pronunciation /tədˈwei̯ljɔɡ/ with an obscure vowel in the first syllable.

However, since the publication in 1957 by the University of Wales, Aberystwyth, of a list of recommended official spellings of Welsh place names, where names are spelt in standard Welsh as a general rule, the form Tudweiliog is now in use on signage, pronounced as /tɨ̞dˈwei̯ljɔɡ/ (the "u" is pronounced as a kind of "i").

The B4413 also links up to the A499 which provides the connection to Pwllheli, where the nearest railway station is situated, along with many other larger stores.

Country music duo John ac Alun were both brought up in the village and attended the local school.