The main changes that occur from the ISO/IEC TR 15504 to ISO/IEC 15504 are as follows:

1. The name change from Software Process Assessment to Process Assessment
2. The restructuring of the standard from 9 parts to 5 parts
3. The inclusion of an exemplar assessment method
4. The removal of the Process Dimension which now resides in an annex to ISO/IEC ISO 12207 and is published as ISO/IEC 12207 AMD1 and AMD2
5. The introduction of the concept of Process Reference Models
6. The revision and alignment of the Capability Dimension with ISO9001: 2000

The major benefit of the change is that it expands substantially the available scope of the standard. Instead of being constrained solely to software life cycle processes, it now defines a common assessment approach that can be applied to any processes.

Within the revised ISO/IEC 15504 process assessment is based on a two dimensional model containing a process dimension and a capability dimension. The process dimension is provided by an external Process Reference Model (PRM), that defines a set of processes characterized by statements of process purpose and process outcomes. The capability dimension consists of a Measurement Framework comprising six Process Capability Levels and their associated Process Attributes. The assessment output consists of a set of process attribute ratings for each process assessed, termed the Process Profile, and may also include the capability level achieved by that process.

The capability dimension has been updated to address some weaknesses highlighted through use of ISO/IEC TR 15504 and also to fully align with the concepts in the published process oriented ISO 9001:2000. The initial input of changes for the alignment of the capability dimension to ISO 9000:2000 resulted from a study performed by the European SPACE Agency into the application of process assessment techniques to quality management systems.

Apart from minor changes in the wording and ordering of process attributes in the measurement framework, the major changes are in the detail of the measurement framework at levels 2 and 3. Much greater detail has been incorporated, and more formal traceability to ISO 9001:2000 has been included. The distinction between process definition and process deployment has also been made at level 3. At levels 4 and 5 the levels have been reworked to clarify the relationship between “Process Capability” as defined in ISO/IEC 15504, and conventional concepts of Statistical Process Control. Level 4 (the Predictable Process) is concerned with the ability to identify and address special causes of process variation. Level 5 (the Optimizing Process) is concerned with the ability to identify and address common causes of process variation.