Unwritten law is law that has not been enacted by the legislature (Parliament and the State Assemblies) and this law is not found in the written Federal and State Constitutions. This law is found in cases, which have been decided by the courts and local customs.
Unwritten law is mainly comprised of:
1. English Law
English law forms part of the laws of Malaysia. English law can be found in the English common law and rules of equity. However, not all of England’s common law and rules of equity form part of Malaysian law.
Section 3(1) of the Civil Law Act 1956 (Revised 1972) provides that, in Peninsular Malaysia, the courts shall apply the common law of England and the rules of equity as administered in England on 7 April 1956. Section 3(1) (b) and Section 3(1) (c) of Civil Law Act 1956 states that in Sabah and Sarawak, the courts shall be relevant the common law of England and the rules of equity, together with statutes of general application, as administered or in force in England on 1 December 1951 and 12 December 1949 accordingly.
But it is not stated that the Common Law and Law of Equity in Malaysia should remain unmodified and follow the same law as administered in England. Common law and law of equity in Malaysia should be developed and amended according to the local needs. In addition, these two laws should also take into account of changes in these laws in England. However, Malaysian government can set their own scope for the amended or repealed Common Law and Law of Equity in Malaysia.
In the case of Mokhtar v Arumugam  MLJ 232, Smith J in a dictum said that the court could not award damages in the nature of interest for delay in the return of specific goods on the basis that such relief had been provided by section 29 of the Civil Procedure Act 1833 (English). He added that by of section 3(1) of the Civil Law Ordinance 1956, such relief, being a creature of English statute, is not available here.
The judge in Smith Kline & French Laboratories Ltd v Salim (Malaysia) Sdn Bhd  2 MLJ 380, stated obiter that if it were found that the general provisions of imported legislation were inapplicable in the country, the courts had the jurisdiction, and would not hesitate to exercise such jurisdiction, to strike down such inapplicable law on the principle lex non cogit impossibilia.
The Supreme Court in Karpal Singh & Anor v Public Prosecutor  2 MLJ 544, held to the effect that English law cannot be applied in criminal procedure, which, in Malaysia, is governed by the Criminal Procedure Code.
No such problem exists in Sabah and Sarawak as it is clearly provided that common law and equity are to be applied ‘together with statutes of general application’. However, the relevance of the law of England throughout Malaysia is subject to two limitations. First, it is applied only in the absence of local statutes on the particular subjects. Local law takes precedence over English law as the latter is only meant to fill in the lacuna in the legal system in Malaysia. Secondly, only the part of the English law that is suited to local circumstances will be applied—proviso to section 3(1), Civil Law Act 1956.
Common law can apply in the absence of local legislation. Local law is regarded highly that the English law. The English law is only meant to fill in the lacuna, in which the local legislation is not present. Only the relevant part which is suited to the local needs and circumstances applies. Malaysia is made up of different races, each possessing their own customs, different from English law. The entire importation of English law means that the sovereignty of local race is affected.
2. Judicial Decision
Malaysian law can also be found in the judicial decisions of the High Court, Court of Appeal and the Federal Court, the then Supreme Court and the Judicial Committee of the Privy Council. Judicial decisions are based on ‘doctrine of binding precedent’. Precedents are the decisions made by judges previously in similar circumstances
Mandatory precedent is applied when the decisions of superior court are binding on lower courts or the superior courts are bound by their own decisions previously. However, the decisions of lower courts are not binding over superior courts. The lower courts must refer to the mandatory precedents of superior courts. However, judge of superior court will make a distinction a case before him and the cases laying down the precedents and can decide not to follow the mandatory precedent if he thinks that the mandatory precedent is not related to the case before him. From this, an original precedent is formed.
Persuasive precedent is a precedent which is useful or relevant to a case. It is not mandatory for the judges to pertain persuasive precedent. Persuasive precedent may be binding on lower courts if judges of superior court choose to apply persuasive precedent.
Customs are another important source of unwritten law. Customs are inherited from one generation to another generation. Every race has its own customs. Chinese and Hindus customs are governed by Chinese and Hindu Customary Law. Natives in Sabah and Sarawak have their own customary law which relates to the land and family matters. ‘Adat’ applies to Malays. There are two types of Adat; Adat Perpatih and Adat Temenggung.
The adat perpatih is prevalent among Malays in Negeri Sembilan and Naning in Malacca. The unique characteristic of Adat Perpatih is matrilineal form of organization. It concerns with matters such as land tenure, lineage, inheritance and election of members of lembaga and YDP. Matrilineal is a system in which one belongs to mother's lineage; it generally involves the inheritance of property, names or titles from mother to daughters.
The other states practice that adat tememggong. The adat temenggong, which originated from Palembang, Sumantra expands a patrilineal system of law. Patrilineal is a system in which one belongs to father's lineage; it generally involves the inheritance of property, names or titles from father to sons.
After the establishment of Law Reform (Marriage and Divorce) Act 1976, the family law has been given enforcement on matters of marriage, divorce and inheritance. As a result, the Chinese and Hindu Customary Laws have lost its effect as an important source of unwritten law in Malaysia