A lallation (also called cambia-letras or troca-letra, "letter changer", in Latin American countries) is an imperfect enunciation of the letter "L", in which it sounds like "R" (or vice versa), as frequently found in infantile speech.

The speech pattern has been particularly associated with the use of the Portuguese, Spanish and English languages by Chinese, Korean, and Japanese people. The use of lallation has thus been a common feature of Western stereotypes of East Asian people. It is also common among English-speakers in parts of East Africa.

Lambdacism (from the Greek letter "λ") is a medical condition or speech impediment related to the pronunciation of /l/ or related phonemes.

A common form of lambdacism is lallation, the substitution of /l/ for /ɹ/ in pronunciation. It is a common feature of Japanese and Korean pronunciation of English. Substitution of /l/ for /n/ at the beginning of a word or syllable (or the reverse at the end) is also a feature in certain East Asian languages, such as Cantonese and Thai.