Periods are omnipresent in writing; they appear at the end of sentences, they pause lists or definitions, and they appear in abbreviations. For the most part, you can think of a period as providing a full stop to a sentence and as tidily ending an abbreviation. A period belongs at the end of a declarative sentence, like the one you’re reading, or at the end of an imperative sentence, like “Click Run to execute the macro.” Most of the time, quotation marks belong outside the period and parenthesis belong inside (see my previous blogs on these subjects). Except with quotation marks, parenthesis, and commas, you won’t need a period if you have another form of punctuation. Drop the period in an abbreviation if it immediately precedes a colon or semi-colon, for instance. Like this: The company was called Purple People Plotters, Inc; it took a while to get the business incorporated. If an abbreviation stands for a single word and is not an acronym, it gets a period at the end, like Dr. or Co. Acronyms take the initial letter of each word in a series to spell out a new word, and don’t get any periods anywhere (like CMOS or HTML). There are some abbreviations that no longer take periods for some reason, like mph, ID, or lb, although no one will fault you if you use a period (m.p.h., Id., and lb., respectively). If the last word in your sentence is an abbreviation, only one period is necessary. So this is correct: She survived by eating fruit such as bananas, apples, pears, etc. Letters and numbers signifying itemization in lists, including Roman numerals, require periods (rather than a colon, typically). Like this: 1. Dust 2. Vacuum 3. Clean frog bowl. 4. Grocery store Notice that the third element, which is an imperative sentence, gets a period at the end. Enumerated lists that are titles require colons, not periods, like this: Exercise 1: Taming the Wild Purple People Plotter Exercise 2: Starting Simply Don’t use a period after a title or heading of any level, and figure captions or table headings only get periods if they are complete sentences. Some publishers prefer complete sentences in their figure captions. Narrative elements in lists, whether bulleted or numbered, do not get periods unless they are complete sentences, or if you need to signify the end of a fragment before beginning an expository complete sentence. Like this: Normalization: a way of ensuring unique data in a database by avoiding redundancy. There are five normal forms of increasing narrowness, allowing developers to design tables that do not duplicate information from other tables and simplifying querying and updating. An ellipsis indicates an unfinished thought or omitted material in a quotation and uses three periods. If your sentence ends with an ellipsis, use four periods. Oh, and gang? Since the invention of the word processor in the 1980s, capable of sensing whether or not there is a serif on the font and adjusting automatically, there is only one space after periods. The two spaces were from the old days of metal plate typesetting, when most fonts had a serif. Please join us in the twenty- first century and save your editor a lot of aggravation pulling out all those empty spaces.