Plain language is an approach to writing and design that makes information easy for its intended audience to find, understand on first reading or hearing, and use. The core idea is audience‑focused clarity across wording, structure, and presentation. ISO formalized this in ISO 24495‑1:2023, a global standard that sets governing principles and guidelines for plain language in printed and digital texts. According to the International Organization for Standardization, the standard applies across languages and genres and emphasizes user needs over writer preferences. It also notes that accessibility guidance such as the Web Content Accessibility Guidelines (WCAG) may be relevant when creating digital documents. ISO 24495‑1.

History and development

• –Early advocacy drew on readability research and public‑sector style guidance. In the United Kingdom, civil servant Ernest Gowers wrote Plain Words (1948) for officials; the combined and expanded edition, The Complete Plain Words (1954), has remained in print and was most recently revised in 2014. Penguin Books.
• –In the United States, readability formulas influenced practice, notably work by Rudolf Flesch (Flesch Reading Ease, 1948) and later the Flesch–Kincaid Grade Level from U.S. Navy research (1975). See the classic 1948 Journal of Applied Psychology paper and the Navy’s 1975 technical report. OA.mg; University of Central Florida repository.
• –In legal and regulatory communication, the U.S. Securities and Exchange Commission adopted Rule 421(d) (“plain English” rule) in 1998, requiring the cover, summary, and risk factors of prospectuses to use short sentences, active voice, everyday words, and reader‑friendly design; the SEC also issued A Plain English Handbook for filers. SEC – Plain English Disclosure; Federal Register; SEC – A Plain English Handbook.
• –Internationally, plain language is recognized in human‑rights frameworks. The United Nations Convention on the Rights of Persons with Disabilities (CRPD) includes “plain-language” within its definition of “communication,” underscoring its role in accessibility. United Nations – CRPD Article 2.

Laws, policies, and standards

• –United States. The Plain Writing Act of 2010 (Public Law 111‑274) requires federal agencies to write “clear Government communication that the public can understand and use” for documents that help the public obtain benefits or comply with requirements; the Office of Management and Budget issued implementation guidance (M‑11‑15) in April 2011. Congress.gov; White House OMB – Memoranda; see also agency pages reinforcing use of the Federal Plain Language Guidelines. Digital.gov; National Archives – Top 10 Principles.
• –New Zealand. The Plain Language Act 2022 requires plain language in specified public‑facing documents and defines plain language as appropriate to the audience, “clear, concise, and well organised.” In 2025, a Plain Language Act Repeal Bill passed its first reading; the Act remained in force pending further stages. New Zealand Legislation; NZ Parliament Hansard – First Reading, 1 April 2025.
• –Canada. Accessibility Standards Canada published CAN‑ASC‑3.1:2025, the country’s first national plain language standard, aligned with federal communications policy and offered free in accessible formats. Government of Canada – Accessibility Standards Canada.
• –European Union. The European Commission runs “Clear writing for Europe,” promoting shorter, simpler, jargon‑free texts and offering guidance and training across EU languages. European Commission – Clear writing for Europe.
• –United Kingdom. Government digital guidance makes plain English mandatory for GOV.UK content and provides a style guide and “words to avoid.” GOV.UK – Content design: Writing for GOV.UK; GOV.UK – Style guide.
• –Australia. The Australian Government Style Manual provides detailed plain‑language guidance on word choice, sentence structure, active voice, and inclusive language. Australian Government – Style Manual; Plain language and word choice.
• –Global standardization. ISO 24495‑1:2023 establishes the governing principles for plain language and points authors of digital content to WCAG and related accessibility standards. ISO 24495‑1.

Principles and techniques

Plain language centers on user needs and outcomes. Commonly cited techniques include writing for the reader, stating key points first, using active voice, favoring short sentences and everyday words (explaining necessary technical terms), organizing content with clear headings and lists, and designing pages for scanning. U.S. federal guidance and training summarize these practices and encourage testing with representative users. National Archives – Top 10 Principles; Digital.gov – Introduction to plain language; CDC – Plain language resources.

Measurement, testing, and limitations

Readability formulas such as Flesch Reading Ease (1948) and Flesch–Kincaid Grade Level (1975) estimate difficulty from surface features (sentence length, syllables) and remain widely used, but research and practice caution against relying on scores alone. Studies in health and education have found weak alignment between formula outputs and reader‑perceived difficulty, supporting direct usability testing with intended audiences as a better indicator of plainness and effectiveness. OA.mg – Flesch 1948; UCF – Kincaid et al. 1975; J Med Internet Research; NC State News; Center for Plain Language. Recent analyses similarly favor reader‑focused evaluation over legacy formulas and note that accessibility and design features influence comprehension beyond lexicon and syntax. Center for Plain Language; ISO 24495‑1.

Applications by sector

• –Government. The U.S. Plain Writing Act mandates plain language in public‑facing materials that help people obtain services or meet requirements; OMB’s M‑11‑15 memo sets implementation steps (senior officials, training, reporting), and agencies publish guidance and reports. Congress.gov; OMB M‑11‑15; Digital.gov. Similar commitments appear in EU and Commonwealth guidance and national standards. European Commission – Clear writing; Australian Style Manual; GOV.UK guidance.
• –Finance and securities. The SEC’s rule and handbook aimed to make prospectuses clearer for investors; empirical work finds the 1998 rule influenced disclosure style beyond prospectuses. SEC – Plain English Disclosure; Journal of Regulatory Economics.
• –Health. U.S. health agencies link plain language to health literacy and equitable access, recommending audience‑appropriate wording, clear structure, and testing with users. CDC – Guidelines, laws & standards.
• –Accessibility and rights. The CRPD’s inclusion of plain language within “communication” underlines its use in removing barriers for people with disabilities, and government guidance often aligns plain language with accessibility obligations. United Nations – CRPD Article 2; Australian Style Manual – Accessibility and reading level.

Organizations and professional community

Professional networks promote research, standards, and practice. Plain Language Association International (PLAIN) connects practitioners in 30+ countries and helped establish International Plain Language Day (13 October). The International Plain Language Federation (founded by PLAIN, Clarity, and the Center for Plain Language) coordinated development of the ISO standard and supports training and certification initiatives. PLAIN; PLAIN – International Plain Language Day; International Plain Language Federation.

Selected definitions and scope

• –ISO: Plain language is achieved when wording, structure, and design enable intended readers to find, understand, and use information. ISO 24495‑1.
• –U.S. statutory definition: “clear, concise, well‑organized, and follows other best practices appropriate to the subject or field and intended audience.” Digital.gov – Introduction.
• –GOV.UK: Plain English is mandatory across government content. GOV.UK – Writing for GOV.UK.

International observances

International Plain Language Day is observed annually on 13 October to raise awareness of clear communication; the date also marks the signing date of the U.S. Plain Writing Act (October 13, 2010). PLAIN; GSA blog.

Related standards and guidance

Plain language efforts often intersect with accessibility and usability standards. For digital content, authors commonly reference WCAG to ensure perceivable, operable, understandable, and robust content; ISO 24495‑1 notes this linkage. ISO 24495‑1.