AS (or similar) may refer to:

• A. S. (automobile), a small French car in the 1920s
• ActionScript, a programming language originally developed by Macromedia and currently by Adobe for developing Flash and Flex applications
• as (Unix), generic name for the assembler program as used on Unix systems
• Aggregate supply, the total supply of goods, in economics
• Almost surely or a.s., in probability theory, an event with probability 1
• Associate of Science, an American Associate's degree
• Arsenic, chemical symbol "As"
• Australian Standard, usually followed by the standard number
• Autonomous system (Internet), a collection of IP networks
• Arcsecond,  arcminute, a unit of angular measurement
• Attosecond or as, one trillionth (long scale) (10^-18) or one quintillionth (short scale) (10^-18) of a second, a unit of time
• Attosiemens or aS, one trillionth (long scale) (10^-18) or one quintillionth (short scale) (10^-18) of a siemens, a unit of electric conductance
• AS, the hull classification symbol for submarine tenders

Aksjeselskap is the Norwegian term for a stock-based company. It is usually abbreviated AS or A/S, especially when used in company names. An AS is always a limited company, i.e. the owners cannot be held liable for any debt beyond the stock capital. Public companies are called Allmennaksjeselskap or ASA while companies without limited liability are called Ansvarlig selskap or ANS.

In probability theory, one says that an event happens almost surely (sometimes abbreviated as a.s.) if it happens with probability one. The concept is analogous to the concept of "almost everywhere" in measure theory. While there is no difference between almost surely and surely (that is, entirely certain to happen) in many basic probability experiments, the distinction is important in more complex cases relating to some sort of infinity. For instance, the term is often encountered in questions that involve infinite time, regularity properties or infinite-dimensional spaces such as function spaces. Basic examples of use include the law of large numbers (strong form) or continuity of Brownian paths.