Lammi (, also ) is a former municipality of Finland. It was consolidated with Hämeenlinna on 2009-01-01.
It is located in the province of Southern Finland and is part of the Kanta-Häme region. The municipality had a population of 5,507 (2008) and covered an area of 611.24 kmò, of which 73.69 kmò is water. The population density is 11 inhabitants per kmò.
Neighbouring municipalities were Asikkala, Hauho, Hausjärvi, Hämeenkoski, Janakkala, Kärkölä, Luopioinen, Padasjoki and Tuulos.
The municipality was unilingually Finnish.
The lake Kuohijärvi is located in Lammi and the lake Pääjärvi is situated at the border between Lammi and Hämeenkoski.