Middle tier logic has been a subject of continuous debate over the years. Should it be stateful or stateless? To what degree should we seek reusability. To what degree should we separate this logic from other layers such as UI and data access. What about services? But despite the debate, the needs of the middle (business) tier have remained the same. Simplify and hide the underlying data structure from the UI. Provide behavior and validation needed by the application and provide the UI (or any other consumer) with easy access to the data. Rockford Lhotka's CSLA is a business object framework that starts at these basic concerns but goes much further. We will take a look at CSLA, exploring some of its more interesting features such as n-level undo, support for data binding in virtually any Microsoft UI technology, and enforcement of business rules and security. From its introduction in Professional Visual Basic 5.0 Business Objects in 1997 to its latest incarnation in Expert C# 2008 Business Objects the CSLA has truly grown up. Carney Calcutt is a Senior Software Engineer at ServiceU Corporation, a Memphis-based application service provider (ASP). ServiceU hosts event management, ticketing, and PCI compliant transaction processing applications via software as a service (SaaS). His primary focus is in middle-tier business object development to support a variety of front ends, including ASP.NET, Silverlight and WCF Services. The bulk of his professional experience is in developing inventory control systems as well as systems that support inventory management and searching. His technical knowledge has centered primarily around Microsoft technologies, with C# being the current language of choice. Carney's non-professional life centers around his family where he and his wife Carol are homeschooling their two children. He is also an aspiring guitarist.