The IAB Ad Unit Guidelines have been developed by the Interactive Advertising Bureau. They are used by marketers, agencies and media companies in the creating, planning, buying and selling of interactive marketing and advertising. The standards are set by the IAB’s Ad Sizes Working Group which meets on a bi-annual basis to review proposed new ad units and issue updated voluntary guidelines as appropriate.

The Interactive Advertising Bureau is comprised of more than 500 media and technology companies who are responsible for selling the majority of online advertising in the United States. Working with its member companies, the IAB evaluates and recommends standards and practices and fields critical research on interactive advertising. Founded in 1996, the IAB is headquartered in New York City with a Public Policy office in Washington, D.C. You’ll find them on the net at http://www.iab.net.

The IAB Standards are voluntary guidelines that provide a framework for ad inventory and web page design. Their goal is to reduce and simplify the amount of work for agencies that may be faced with having to create several assets of a similar size for different publishers.

This works well in most cases as it provides us all with a basic level commonality in advertising, though in niche markets such as the Christian Market that FrontGate Media serves, there are often custom promotions that provide much deeper value through better relationship creation for advertisers, but which go beyond the IAB Standards. Examples would include more aggressive audience interaction through things like contests or custom advertorial.

In those cases, major agencies, particularly the secular market ad agencies working Christian projects, can miss out on great opportunities to create a deeper contact and interaction with Christian target audiences if they are limiting themselves solely to IAB Standards, though we do have plenty of IAB Standard ad options available through FrontGate Media.  

There are a few “headscratchers” in the 2012 update, for example one of my favorite ad sizes, the 300×600 Jumbo Skyscraper, is no longer part of the UAP, and yet that size continues to be popular with advertisers because response rates are typically higher.  Another headscratcher for me are the 125×125 and 250×250 rectangle sizes which have been moved out of the active list.  Those sizes are very popular in the blogosphere, just look at many WordPress sites.

NOTE: All dimensions are in pixels.

Universal Ad Package
As of February 26, 2012

There are MANY more standards and details at the IAB site.  I highly recommend that you browse their site a bit more.