Rutgers University
Rutgers University: Guide to Grammar and Style: Periods
An excellent outline of the usage and rules concerning the "period" in English punctuation. Includes guidelines about acronyms, abbreviations, sentence ending, and more.
Capital Community College Foundation
Guide to Grammar and Writing: The Period
An excellent resource detailing the uses and rules of the grammatical element "the period." Also includes information about the period in sentences, quotation marks, parentheses, and abbreviations.
Other
Sandhills Community College: The Period
A good guide to understanding the several uses of the period in English punctuation. Includes information concerning periods in a sentence as well as abbreviations. Includes several examples.
ACT360 Media
Writing Tips: Punctuation: Period
A brief description of the rules, usage, and examples of the "period" in English punctuation. Includes basic information concerning period use in abbreviations as well.