An Undang is a ruling chief of the state of Negeri Sembilan, in Malaysia. The name is thought to derive from the Malay word undang-undang meaning law.

Traditionally, the Minangkabau who settled in Negeri Sembilan, Malaysia at the end of the 17th Century choose from amongst themselves a "penghulu" or headman. Several of these "penghulus", notably that of Sungai Ujong, Jelebu, Johol and Rembau became powerful enough to exalt themselves above other "penghulus". By the early part of the 18th Century, the leaders of these four districts started calling themselves "Undang".

Malaysia's modern day constitution confirms the status of the Undang under Article 181. Undangs are still chosen from amongst certain noble families in the state, the succession being both matrilineal and elective.

Though now only symbolically powerful, the Undangs still carry out duties such as attending the state opening of the legislative assembly and electing the Yang di-Pertuan Besar or head of state.

Each of the four Undangs have different titles. They are:

1. Sungai Ujong: Ke Bawah Kaus Yang Teramat Mulia Datuk Kelana Jaya Putera
2. Jelebu: Ke Bawah Kaus Yang Amat Mulia Datuk Mandulika Menteri Akhirulzaman Sultan Jelebu
3. Johol: Ke Bawah Kaus Yang Amat Mulia Datuk Johan Pahlawan Lela Perkasa Sitiawan
4. Rembau: alternating between Ke Bawah Kaus Yang Amat Mulia Datuk Lela Maharaja (current) and Ke Bawah Kaus Yang Amat Mulia Datuk Sedia Raja

The senior wife of an Undang has the honorific title of "To' Puan".