Why are Workflow Standards Relevant?
Organizations making an investment in workflow software want to be sure that their investment is going to be protected. With standards users can have confidence that essential criteria will be met, hence reducing the risk involved. This clearly becomes of paramount importance when workflow systems are required to interoperate with those of other organizations whenever business processes are conducted across organizational boundaries.
Workflow Standards Framework
The Coalition has developed a framework for the establishment of workflow standards. This framework includes five categories of interoperability and communication standards that will allow multiple workflow products to coexist and interoperate within a user's environment. More technical details are available in the WfMC document
Workflow Reference Model. Document Number TC00-1003 (pdf)
Workflow Reference Model Diagram
Click on diagram to view larger version

For the complete list of all interfaces, please visit http://www.wfmc.org/standards/docs.htm
Highlights:
Workgroup 1: XPDL
Workgroup 4: Wf-XML
Technical Committee and Working Groups