What is Chain of Command in D365? Chain of Command is the term that describes how we customize, or extend, base Microsoft code in Microsoft Dynamics 365. Microsoft's base objects and code cannot be changed directly in D365. However, we are able to make changes to separate objects and classes that are then combined with the existing base object to form the final version. Learn the fundamentals of how to use Chain of Command for classes, tables, and form code. As well as some of the tips for accessing variables, controls, and datasources within Chain of Command methods.