This report describes a textual requirement specification language, called ReqSpec, for the Architecture Analysis & Design Language (AADL). It is based on the draft Requirements Definition and Analysis Language Annex, which defines a meta-model for requirement specification as an-notations to AADL models. A set of plug-ins to the Open Source AADL Tool Environment (OSATE) toolset supports the ReqSpec language. Users can follow an architecture-led requirement specification process that uses AADL models to represent the system in its operational con-text as well as the architecture of the system of interest. ReqSpec can also be used to represent existing stakeholder and system requirement documents. Requirement documents represented in the Requirements Interchange Format can be imported into OSATE to migrate such documents into an architecture-centric virtual integration process. Finally, ReqSpec is an element of an architecture-led, incremental approach to system assurance. In this approach, requirements specifications are complemented with verification plans. When executed, these plans produce evidence that a system implementation satisfies the requirements. This report introduces the ReqSpec notation and illustrates its use on an example.