The success of a project, program, or portfolio realization is dependent on cooperation between a project manager/team project and stakeholders. This cooperation can be provided via a blended mental space; the main function of it is interaction and communication support of all participants in the project process throughout the project lifecycle. The blended mental space building requires creation of the specific methodology, which is based on the technical maturity models used. In the frame of the chapter, two new organizational maturity models are described. They are offered by IPMA through its internationally widespread member associations: IPMA Delta for assessing and developing project management maturity and the IPMA Organizational Competence Baseline (OCB), acting as a reference model for IPMA Delta. In addition to this description, a case study reveals insights into the usage of IPMA Delta and the benefits realized through a holistic assessment of project management maturity.