ECOCITIES is an energy optimization system for building portfolios combining and extending the benefits of Energy Management Software (EMS), Computer-aided Facility Management (CAFM) software and building portfolio management software. It integrates building administration and monitoring, energy accounting and building portfolio optimization. Thereby, it supports the definition of low carbon action plans in terms of environmental impact (e.g., carbon footprint, energy efficiency) and financial impact (e.g., investment costs, running, costs).