ISO/IEC 15504 (all parts) provides a framework for the assessment of processes. This framework can be used by organizations involved in planning, managing, monitoring, controlling and improving the acquisition, supply, development, operation, evolution and support of products and services.
ISO/IEC 15504-3:2004 provides guidance on meeting the minimum set of requirements for performing an assessment contained in ISO/IEC 15504-2.
It provides an overview of process assessment and interprets the requirements through the provision of guidance on:

1. performing an assessment;
2. the measurement framework for process capability;
3. process reference models and process assessment models;
4. selecting and using assessment tools;
5. competency of assessors;
6. verification of conformity.

ISO/IEC 15504-3:2004 also provides an exemplar documented assessment process that conforms to the requirements of 4.2 in ISO/IEC 15504-2.