that is, to determine the extent to which retail e-commerce involves sales to customers in states where the seller has nexus or is, for whatever reason, collecting sales taxes. To do so, we began by researching the firms listed in the 2009 edition of Internet Retailer Top 500 Guide, which provides data on 2008 retail e-commerce sales by the largest online retailers, or all those with annual online sales exceeding $9 million.