An outline, also called an hierarchical outline, is a list arranged to show hierarchical relationships and is a type of tree structure. It is used to present the main points or topics of a given subject, often used as a rough draft or summary of the content of a document.
Writers of fiction and creative nonfiction, such as Jon Franklin, may use outlines to establish plot sequence, character development and dramatic flow of a story, sometimes in conjunction with free writing.
Merriam-Webster's manual for writers and editors (1998, p. 290) recommends that the section headings of an article should, when read in isolation, combine to form an outline of the article content. Garson (2002) distinguishes a 'standard outline', presented as a regular table of contents from a refined tree-like 'hierarchical outline', stating that "such an outline might be appropriate, for instance, when the purpose is taxonomic (placing observed phenomena into an exhaustive set of categories). ... hierarchical outlines are rare in quantitative writing, and the researcher is well advised to stick to the standard outline unless there are compelling reasons not to."
 Outline organization
An outline is a list of items, organized according to some consistent principle. Each item may be divided into additional sub-items. Each organizational level in an outline has at least two subcategories as advised by major style manuals in current use.
 Types of outlines
 Outline styles
 Sentence outline
A sentence outline is a hierarchical outline composed of sentences. Each includes a heading or single sentence of a planned document about the subject of the outline. It is the type of outline typically used to plan the composition of books, stories, and essays. It can also be used as a publishing format, in which the outline itself is the end product.
 Topic outline
A topic outline is a hierarchical outline composed of topics. Each entry is a subtopic of the subject of the outline. One application of topic outlines is the college course overview, provided by professors to their students, to describe the scope of the course. Another application is as a subject outline, such as for an encyclopedia.
 A sample topic outline application: An outline of human knowledge
Propædia is the historical attempt of the Encyclopædia Britannica of presenting a hierarchical "Outline of Knowledge" in a separate volume in the 15th edition of 1974. The "Outline of Knowledge" was a project by Mortimer Adler. Propædia had three levels, 10 "Parts" at the top level, 41 "Divisions" at the middle level and 167 "Sections" at the bottom level, numbered, for example "1. Matter and Energy", "1.1 Atoms", "1.1.1. Structure and Properties of Atoms".
 Outlines with prefixes
A feature included in many outlines is prefixing. Similar to section numbers, an outline prefix is a label (usually alphanumeric or numeric) placed at the beginning of an outline entry to assist in referring to it.
 Bare outlines
Bare outlines include no prefix.
 Alphanumeric outline
An alphanumeric outline includes a prefix at the beginning of each topic as a reference aid. The prefix is in the form of roman numerals for the top level, upper-case letters (in the alphabet of the language being used) for the next level, Arabic numerals for the next level, and then lowercase letters for the next level. For further levels, the order is started over again. Each numeral or letter is followed by a period, and each item is capitalized, as in the following sample:
Thesis statement: E-mail and internet monitoring, as currently practiced, is an invasion of employees' rights in the workplace.
- I. The situation: Over 80% of today's companies monitor their employees.
- A. To prevent fraudulent activities, theft, and other workplace related violations.
- B. To more efficiently monitor employee productivity.
- C. To prevent any legal liabilities due to harassing or offensive communications.
- II. What are employees' privacy rights when it comes to electronic monitoring and surveillance in the workplace?
- A. American employees have basically no legal protection from mean and snooping bosses.
- 1. There are no federal or State laws protecting employees.
- 2. Employees may assert privacy protection for their own personal effects.
- B. Most managers believe that there is no right to privacy in the workplace.
- 1. Workplace communications should be about work; anything else is a misuse of company equipment and company time
- 2. Employers have a right to prevent misuse by monitoring employee communications
Some call the Roman numerals "A-heads" (for "A-level headings"), the upper-case letters, "B-heads", and so on. Some writers also prefer to insert a blank line between the A-heads and B-heads, while often keeping the B-heads and C-heads together.
If more levels of outline are needed, lower-case Roman numerals and numbers and lower-case letters, sometimes with single and double parenthesis can be used, although the exact order is not well defined, and usage varies widely.
The scheme recommended by the MLA Handbook, and the Purdue Online Writing Lab, among others, uses the usual five levels, as described above, then repeats the Arabic numerals and lower-case letter surrounded by parentheses (round brackets) – I. A. 1. a. i. (1) (a) – and does not specify any lower levels, though "(i)" is usually next. In common practice, lower levels yet are usually Arabic numerals and lower-case letters again, and sometimes lower-case Roman again, with single parentheses – 1) a) i) – but usage varies. MLA style is sometimes incorrectly referred to as APA style, but the APA Publication Manual does not address outline formatting at all.
A very different style recommended by The Chicago Manual of Style, based on the practice of the United States Congress in drafting legislation, suggests the following sequence, from the top to the seventh level (the only ones specified): I. A. 1. a) (1) (a) i) – capital Roman numerals with a period, capital letters with a period, Arabic numerals with a period, italic lowercase letters with a single parenthesis, Arabic numerals with a double parenthesis, italic lowercase letters with a double parenthesis, and italic lowercase Roman numerals with a single parentheses, though the italics are not required). Because of its use in the US Code and other US law books, Many American lawyers consequently use this outline format.
Another alternative scheme repeats all five levels with a single parenthesis for the second five – I) A) 1) a) i) – and then again with a double parenthesis for the third five – (I) (A) (1) (a) (i).
One side effect of the use of both Roman numerals and upper-case letters in all of these styles of outlining is that, in most alphabets, "I." may be an item at both the top (A-head) and second (B-head) levels. This is usually not problematic, because lower level items are usually referred to hierarchically. For example, the third sub-sub-item of the fourth sub-item of the second item is item II. D. 3. So, the ninth sub-item (letter-I) of the first item (Roman-I) is item I. I., and only the top level one is item I.
 Decimal outline
The decimal outline format has the advantage of showing how every item at every level relates to the whole, as shown in the following sample outline:
Thesis statement: ---
- 1.0 Introduction
- 1.1 Brief history of Liz Claiborne
- 1.2 Corporate environment
- 2.0 Career opportunities
- 2.1 Operations management
- 2.1.1 Traffic
- 2.1.2 International trade and corporate customs
- 2.1.3 Distribution
- 2.2 Product development
 See also
- Outline of knowledge
- Outliner (software used to create outlines)
- Abstract (summary)
- Concept map
- Mind map
- Topic Map
- Tree structure
- "Lists and Outlines (6.121–126)". Chicago Manual of Style (16th ed.). Chicago: U. of Chicago Press. 2010.
- OED: "outline n.3.a. In pl. The main features or general principles of a subject, proposal, etc. 3.b. A brief verbal or written description of something, giving a general idea of the whole but leaving details to be filled in; a rough draft, a summary. Also: a précis of a proposed article, novel, scenario, etc."
- Writing for Story, Penguin, 1994
- G. David Garson, Guide to writing empirical papers, theses, and dissertations. CRC Press, 2002, ISBN 978-0-8247-0605-0, chapter "Typical Outlines", pp. 23-34.
- The following is certainly not an exhaustive list of relevant style guides:
- Turabian, K. L (2003). A Manual for Writers of Research Papers, Theses, and Dissertations (7th ed.). Chicago: U. of Chicago Press. pp. 63–64. "You should have at least two items to list at each level; if you do not, reconsider the structure of the outline."
- Gibaldi, J (2003). MLA Handbook for Writers of Research Papers (6th ed.). New York: Modern Language Association of America. p. 53. "Logic requires that there be a II to complement a I, a B to complement an A, and so on."
- Tardiff, Elyssa; Brizee, Allen (2010.01.08). "Four Main Components for Effective Outlines". Retrieved 2010-04-02. "Division - How do I accomplish this? Each heading should be divided into 2 or more parts."
- "How to Make an Outline". Psychology Writing Center, U. of Washington. Retrieved 2010-04-02. "Both topic and sentence outlines follow rigid formats... By convention, each category consists of a minimum of two entries."
- "How to Write an Outline". Los Angeles City College Library Online. Retrieved 2010-04-02. "Each heading and subheading must have at least two parts."
- "1.8.3: Final Outline". MLA Handbook for Writers of Research Papers (Seventh ed.). New York, NY: Modern Language Association of America. 2009. p. 45. ISBN 978-1-60329-024-1.
- "Developing an Outline". Purdue Online Writing Lab. Purdue University. 2011 [last update]. Retrieved 2011-10-20.
- For example: "APA Outline Format Examples". YourDictionary.com. 2011 [last update]. Retrieved 20 October 2011.
- "Lists and Outline Style (6.124–130)". Chicago Manual of Style (15th ed.). Chicago, IL: U. of Chicago Press. 2003. pp. 270–275. ISBN 0-226-10403-6.
- Mary Ellen Guffey, "Organizing and Writing Business Messages," Business Communication: Process and Product, p. 160-161.
- "Numbers: Lists and Outlines," Manual for Writers and Editors (Merriam-Webster, Incorporated: 1998), p. 103.
- White, Basil (1996) Developing Products and Their Rhetoric from a Single Hierarchical Model, 1996 Proceedings of the Annual Conference of the Society for Technical Communication, 43, 223-224. 
- OWL: Online Writing Lab, Purdue University
- "Report writing," Britannica Student Encyclopedia, Encyclopædia Britannica Online (Accessed January 5, 2006)
- William E. Coles, Jr. "Outline," World Book Online (Accessed January 5, 2006)
- Ted Goranson's About this Particular Outliner 'Outlining and Styles'
- Jon Franklin "Writing for Story", Penguin 1994.