PM² is a project management methodology developed and supported by the European Commission. Its purpose is to enable project teams to manage their projects effectively and deliver solutions and benefits to their organisations and stakeholders. PM² is light, easy to implement and suitable for any project. PM² has been custom developed with the needs, culture and constraints of the EU institutions in mind, while incorporating elements from globally accepted standards and best practices. Open PM² is an initiative that brings the methodology and its benefits closer to the user community by providing open access to PM² to EU Member States, private companies and the citizens at large. This third edition of the PM² Guide, supported by the EC ISA² Programme, includes the following changes: The internal EC edition and the Open one have been merged in a single publication. Important appendices have been added to enable adopting organisations to manage portfolios, programmes and projects. A selection of efficient tools for project managers have been included focusing on optimal management behaviours. PM² maintains a strong bond with the domain-specific Agile methods such as PM² – Agile. The PM² guide provides: a project governance model (i.e. roles & responsibilities); a project lifecycle (i.e. project phases); a set of processes (i.e. project management activities); a set of project artefacts (i.e. templates and guidelines); a set of mindsets (i.e. effective beliefs and behaviours).