Luilang, or ambiguously Ketagalan (Ketangalan, Tangalan; Chinese: 凱達格蘭語; pinyin: Kǎidágélányǔ), was a Formosan language spoken south of modern-day Taipei in northern Taiwan by one of several peoples that have been called Ketagalan.

According to oral tradition, the Luilang people originally inhabited four villages near Taipei: Luili (雷里, Leili), Siulang (秀朗, Xiulang), Bulisiat (務裡薛, Wulixue) and Liau-a (了阿, Liao'a).

These merged under the combined name Luilang (雷朗, Leilang), and later migrated to their current location in Outer Oat-a (外挖仔庄, Waiwazizhuang) in the 18th century.

However, that name is ambiguous, originally referring to all of plains tribes of northern Taiwan.

There has been argument in the literature as to whether it is better applied to Luilang, to the south and west of Taipei, or to Basay, to the east.