正当法律程序（due process 或 due process of law）为一个重要的法律原则，其主要源自于英美法系的国家，其内容为，政府必须要尊重任何依据国内法赋予给人民的法律上之权利，而非仅尊重其中一部分或大部分的权利。在美国，随着案例法的逐渐发展，本原则给予了个人相当大的能力在对抗政府或机关暴力以实现个人权利，而此原则通常不会被拿来对抗其他个人。
正当法律程序也常被用来解释为实体法或程序法上的限制，用以规律法官“司法权”（而非国会“立法权”）界定和保障平等权、自由权这些人民的基本权利。不过此种解释具有一定的争议性，且其与自然正义法则以及程序正义这两个被用于其他法域的概念相类似。
正当法律程序，最早起源于英国的大宪章，之后移植到美国，在美国宪法修正案中具体呈现。
美国宪法修正第五条及第十四条，规定了除经过正当法定程序，不得剥夺任何人之生命、自由或财产。前者适用于联邦，后者则拘束各州。但是在美国宪法中，并没有明文规则何谓“正当法律程序”，而是交由联邦法院，于具体案件发生时，根据其不同情事，做出判决。
美国宪法第五修正案规定：
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No person shall be ... deprived of life, liberty, or property, without due process of law ....
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译文：未经正当法律程序，不得剥夺任何人的生命、自由或财产。
美国宪法第十四修正案规定：
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nor shall any State deprive any person of life, liberty, or property, without due process of law ...
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译文：亦不得未经正当法律程序由任何国家剥夺任何人的生命、自由或财产。
在台湾，学者汤德宗认为中华民国宪法第8条便是关于正当法律程序所做出的规定，不过就此仍存在有一定的争议[1]，其规定：
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人民身体之自由应予保障。除现行犯之逮捕由法律另定外，非经司法或警察机关依法定程序，不得逮捕拘禁。非由法院依法定程序，不得审问处罚。非依法定程序之逮捕、拘禁、审问、处罚，得拒绝之。
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“正当法律程序”一词在其于1791年年被订进美国宪法以前便已存在许久。而这个词在英国及美国皆有一段很长的历史可以溯及：
“正当法律程序”这个概念的产生可以被回溯自公元1215年的大宪章。在大宪章的第39章中，英国国王约翰做出了以下的承诺：“任何自由人不得被捉拿、拘囚、剥夺产业，放逐或受任何损害。除非受同等人之合法判决及国法所允许，我们亦不会自己充当军队或派军攻击他。（No free man shall be taken or imprisoned or disseised of his Freehold, or Liberties, or free Customs, or be outlawed, or exiled, or any other wise destroyed, nor will we go upon him nor send upon him, except by the lawful judgment of his peers or by the law of the land.）”[2]而大宪章本身马上就成为“国法”的一部分，大宪章第61章授权给被选举出来的25人男爵团当国王触犯了任何人皆须受到保障的权利时，以多数决纠正之[2]。因此，大宪章借由要求王室必须要服从法律，同时也限制王室如何变更国法，而在英国创设了法治（rule of law）。然而，必须要注意的是，在13世纪时，这些规定的效力可能仅及于地主的权利，而不包含一般的农民或乡村居民在内[3]。
较精简版的大宪章之后由英国国王签署，而大宪章第39条的人数则被改为29人[4]。而“正当法律程序”（due process of law）这个词，首见于公元1354年爱德华三世统治时，关于大宪章的法令：“任何人非经正当法律程序，不得剥夺其土地或住所，不得将其逮捕或监禁，亦不得剥夺其继承权或将其处死。”（No man of what state or condition he be, shall be put out of his lands or tenements nor taken, nor disinherited, nor put to death, without he be brought to answer by due process of law.）[5]
1608年时，英国法学家爱德华·科克所写的专论中，便有讨论到大宪章的定义。科克解释认为，其中的“国法”（the law of the land），是指“判例法、成文法或英格兰的传统...（一言以蔽之）即正当的程序以及法定的程序...”[6]。
在美国法律体系中，正当程序有着重要的位置。它规定以下两条：
- 在公民被控告和索赔之前，必须给予公民通知。
- 在剥夺公民人身自由和所有财产之前，必须给予公民机会反驳控告和索赔。
翁岳生编，行政法（下），台北：元照，2006年，98。.
McKechnie, William Sharp. Magna Carta: A Commentary on the Great Charter of King John. Glasgow: Robert MacLehose and Co., Ltd. 1905: 136–37 [2012-07-08]. （原始内容存档于2017-01-15）.: "The question must be considered an open one; but much might be said in favor of the opinion that 'freeman' as used in the Charter is synonymous with 'freeholder'...."
- Goldberg v. Kelly （页面存档备份，存于互联网档案馆）
- U.S. Constitution: Fifth Amendment. Findlaw. [2009-04-07]. （原始内容存档于2012-05-11）.
- Bernstein, David. Rehabilitating Lochner: Defending Individual Rights against Progressive Reform. Chapter 1. Chicago: University of Chicago Press. 2011. ISBN 0-307-26313-4.
- Breyer, Stephen. Active Liberty: Interpreting Our Democratic Constitution. New York: Knopf. 2005. ISBN 0-307-26313-4.
- Friendly, Henry J. Some Kind of Hearing. University of Pennsylvania Law Review (University of Pennsylvania Law Review, Vol. 123, No. 6). 1975, 123 (6): 1267–1317. JSTOR 3311426. doi:10.2307/3311426.
- Hawkins, Brian. The Glucksberg Renaissance: Substantive Due Process since Lawrence v. Texas (PDF). Michigan Law Review. 2006, 105 (2): 409. （原始内容 (PDF)存档于2007-06-15）.
- Hyman, Andrew. The Little Word 'Due'. Akron Law Review. 2005, 38: 1. （原始内容存档于February 5, 2013）.
- Kadish, Sanford H. Methodology and Criteria in Due Process Adjudication—A Survey and Criticism. Yale Law Journal. 1957, 66 (3): 319–363. JSTOR 793970.
- Madison, P. A. A Dummies Guide to Understanding the Fourteenth Amendment. FederalistBlog.us. 2008. （原始内容存档于2012-05-11）.
- Nowak, John; Rotunda, Ronald. Constitutional Law. West. 2000.
- Orth, John. Due Process of Law: A Brief History. University Press of Kansas. 2003.
- Ring, Kevin. Scalia Dissents: Writings of the Supreme Court's Wittiest, Most Outspoken Justice. Washington: Regnery. 2004. ISBN 0-89526-053-0.
- Shipley, David E. Due Process Rights Before EU Agencies: The Rights of Defense Article discussing the procedural safeguards that have been recognized in the EU and the parallels between procedural due process in the United States and the rights of defense in the EU.
- Sudbury Valley School (1970). Due Process of Law in School. A school where order and discipline is achieved by a dual approach based on a free and democratic framework: a combination of popularly based authority, when rules and regulations are made by the community as a whole, fairly and democratically passed by the entire school community, supervised by a good judicial system for enforcing these laws—due process of law—and developing internal discipline in the members of the community by enhancing their ability to bear responsibility and self-sufficiency.
- Yoshino, Kenji. The Pressure to Cover: The New Civil Rights. The New York Times Magazine. 2006-01-15 [2010-05-01]. （原始内容存档于2016-05-20）. Discussing potential of liberty rights to overtake equality rights.
- Tugend, Alina. Speaking Freely About Politics Can Cost You Your Job. The New York Times. 2015-02-20 [2018-08-19]. （原始内容存档于2021-03-10）. "It’s important to remember that even though private employees don’t have constitutional or federal protection, they do have a due process right."
