Codification means putting laws or rules into a systematic code. The codification process may consist of taking judicial decisions or legislative acts and converting them into codified law. This process does not necessarily create a new law, it merely organizes the existing law, usually by subject, into a code. Recodification refers to a process in which existing codified laws are reformatted and rewritten into a new codified structure. This is often necessary because the legislative process of amending laws and the legal process of interpreting laws over time lead to a code that contains archaic terms, replaced text, and redundant or contradictory laws over time. Due to the size of a typical government code, the legislative process of recodifying a code can often take a decade or more. The rules and regulations promulgated by the agencies of the executive branch of the U.S. federal government are codified as the Code of Federal Regulations. These regulations are authorized by specific enabling statutes adopted by Parliament and generally have the same force as legal law. The first permanent system of codified laws is found in Imperial China,[Note 1] with the compilation of the Tang Code in 624 AD. This formed the basis of the Chinese Penal Code, which was eventually replaced by the Grand Qing Law Code, which in turn was abolished in 1912 after the Xinhai Revolution and the establishment of the Republic of China.
The new laws of the Republic of China were inspired by the German codified work, the Civil Code. A very influential example in Europe was the French Code Napoleon of 1804. For example, in the United States, acts of Congress are codified chronologically in the order in which they became law. The United States Code is the set of all such federal laws. Common law has been codified in many jurisdictions and in many areas of law: criminal codes in many jurisdictions are examples of this, including the California Civil Code and the consolidated laws of New York, New York. English Judge Sir Mackenzie Chalmers is known as the author of the Bills of Exchange Act 1882, the Sale of Goods Act 1893 and the Marine Insurance Act 1906, all of which codified existing common law principles. The Sale of Goods Act was repealed and re-enacted by the Sale of Goods Act 1979 in a way that showed how strong the 1893 original had been. [Note 2] The Marine Insurance Act (slightly amended) has been remarkably successful, adopted verbatim in many common law jurisdictions. Most English criminal laws have been codified, in part because they allow for precision and certainty in the application of the law. However, broad areas of the common law, such as contract law and tort law, remain remarkably unchanged. Over the past 80 years, there have been laws dealing with immediate problems, such as the Law Reform (Frustrated Contracts) Act of 1943 (which, among other things, dealt with war-invalidated treaties) and the Contracts (Rights of Third Parties) Act of 1999, which changed the doctrine of privacy.
However, no progress has been made in the adoption of Harvey McGregor`s (1993) Contract Code, although the Law Commission, in collaboration with the Scottish Law Commission, has asked him to submit a proposal for the full codification and unification of the contract law of England and Scotland. Similarly, codification in tort law was fragmentary at best, a rare example of progress is the Contributory Withended Act of 1945. A notable example of the first was the Lithuanian statutes in the 16th century. The movement for codification gained momentum during the Enlightenment and was implemented in several European countries at the end of the 18th century (see Civil Code). However, it only spread after the adoption of the French Napoleonic Code (1804), which greatly influenced the legal systems of many other countries. In addition, parts of some acts of Congress, such as provisions relating to the date of entry into force of amendments to codified laws, are not codified at all. These Acts can be consulted with reference to the Acts as published in the “Slips Act” and “Session Act” forms. However, commercial publications specializing in legal documents often organize and print laws that are not coded with the codes to which they refer. In addition to religious laws such as halakha, important codifications were developed in the ancient Roman Empire, with compilations of the Lex Duodecim Tabularum and much later the Corpus Juris Civilis. However, these codified laws were the exceptions rather than the rule, for for much of antiquity, Roman laws remained largely uncodified. When interpreting a codified law, courts sometimes refer to the original legislation or legal process to understand the intent of the creator of the law.
Papal attempts to codify the scattered mass of canon law have lasted eight centuries since Gratian produced his decree around 1150.  In the 13th century, canon law in particular became the subject of scientific studies, and Roman popes produced various compilations. The most important of these were the five books of Decretales Gregorii IX and Liber Sextus of Boniface VIII. Legislation has developed over time. Some of this has become obsolete and contradictions have crept in, making it difficult recently to understand what an obligation is and where to find the law on a particular issue. Because every congressional bill can contain laws on a variety of topics, many or parts of it are also reorganized and published in a current thematic codification by the Office of the Law Review Advisor. The official codification of federal laws is called the United States Code. In general, only “public laws” are codified. The Code of the United States is divided into “titles” (based on global topics) numbered from 1 to 54.  Title 18, for example, contains many federal criminal laws. Title 26 is the Internal Revenue Code.
 But even in the form of the law, many laws naturally concern more than one subject. For example, the law that makes tax evasion a crime affects both criminal law and tax law, but is only found in the Internal Revenue Code.  Other tax laws are not found in the Internal Revenue Code, but for example in the Bankruptcy Code in Title 11 of the United States Code or in the Judiciary Code in Title 28. Another example is the national minimum age for alcohol consumption, which is not found in Title 27, Intoxicating Spirits, but in Title 23, Highways, § 158. .