The Undang Yang Empat (Negeri Sembilan Malay: Undang Nan Ompek; Jawi: أوندڠ يڠ امڤت) are the ruling chiefs or territorial chiefs who play an important role in the election of a new Yang di-Pertuan Besar of Negeri Sembilan, Malaysia. The name is believed to be derived from the Malay word undang-undang meaning "law".

The Minangkabau who settled at Negeri Sembilan, in present-day Malaysia at the end of the 17th century ruled by a "penghulu" or headman who was chosen from the noble families of Sakai and Jakun belonging to the Biduanda clan. These "penghulus", notably that of Sungai Ujong, Jelebu, Johol and Rembau became powerful enough to exalt themselves above the other "penghulus". These penghulus later acknowledged by the sultan of the old Johor Empire as a sovereign in their own territory. By the early part of the 18th century, the leaders of these four territories started using the title "Undang" to distinguish themselves from other penghulu luak.

Malaysia's modern day constitution confirms the status of the Undang under Article 71, 160, 181 and the Eight Schedule of Federal Constitution as Malay Ruler within the Federation. Undangs are still chosen from amongst certain noble families in the state, the succession being both matrilineal and elective following the Adat Purbakala.

According to Ernest Woodford Birch, the Undang Yang Empat trace their history and rank back to the four Batins (Sakai Chiefs) of Johol, Sungei Ujong, Jelebu and Klang, with Rembau later taking the position left vacant by Klang.^[1]

The ruling chiefs are selected among the nobility in each luak (district), following matrilineal inheritance, part of the state's adat perpatih customs.

• The Undang of Sungai Ujong is chosen among the Waris Klana di-Hulu and Waris Klana di-Hilir families of the noble House of Waris Klana and inherits the title Dato' Klana Petra.^[2]
• The Undang of Jelebu is elected among the three noble houses of Waris Ulu Jelebu, Waris Sarin and Waris Kemin, and inherits the title Dato' Mendika Menteri Akhirul Zaman.^[2][3]
• Undangs of Johol (Undang of Johol [ms]) are a succession of members of two families in the female line of either Perut Gemencheh or Perut Johol.^[2] The son of the eldest sister of the incumbent is usually the heir. He inherits the title Dato' Johan Pahlawan Lela Perkasa Setiawan.^[2]
• The Undang of Rembau alternates between the two major noble houses in the Luak, namely the Waris Jakun (who on accession inherits the title Dato' Lela Maharaja) and the Waris Jawa (Dato' Sedia Raja).^[2] As with the Undang of Johol, the son of the eldest sister of the incumbent is the heir in the family.^[2]

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

The Undangs carry out duties such as co-head of state, co-head of Islam as state religion, upholding and safeguarding the special position of Bumiputera in Negeri Sembilan, attending the state opening of the legislative assembly and electing the Yang di-Pertuan Besar of Negeri Sembilan, who is also the co-head of state of Negeri Sembilan. The Undangs themselves cannot stand for election and their choice of ruler is limited among the princes of Seri Menanti royal family who are:

• Muslim male
• Malay
• a "lawfully begotten descendant of Raja Radin ibni Raja Lenggang [ms]".