Required Bins : Minimal required assemblies to work with NHibernate Required for LazyLoading : NHibernate 2.1 has a new important feature regarding dynamic-proxy systems for lazy-loading Details are available in releasenotes.txt and in this post http://nhforge.org/blogs/nhibernate/archive/2008/11/09/nh2-1-0-bytecode-providers.aspx