Market mechanisms, such as auctions, will likely rep resent a common interaction medium for agents on the Internet. The Michigan Internet AuctionBot is a flexible, scalable, and robust auction server that supports both software and human agents. The server manages many aimultancous auctions by separating the interface from the core auction procedures. This design provides a responsive interface and tolerates system and network disruptions, but necessitates careful timekeeping procedures to ensure temporal accuracy. The AuctionBot has been used extensively in classroom exercises, and is available to the general Internet population. Its flexible specification of auctions in terms of orthogonal parameters makes it a useful device for agent researchers exploring the design space of auction mechanisms.