**Preface to "Net-Zero/Positive Energy Buildings and Districts"**

Buildings account for more than one-third of the global final energy consumption and CO2 emissions. The building sector offers a significant potential in the transition towards the decarbonisation of societies. To achieve this goal, different concepts and implementations of Net-Zero/Positive Energy Buildings and Districts (NZPEBD) have emerged in recent years and are still in progress. Countries around the world have adapted different strategies and regulations for the decarbonisation of the building sector. An example is the EU Directive on Energy Performance of Buildings (EPBD) legislation that aims at achieving Nearly Zero Energy Buildings. Another example is the European Strategic Energy Technology (SET) Plan that supports the planning, deployment, and replication of 100 Positive Energy Neighbourhoods by 2025.

The concept of NZPEBD is not only about achieving a net or positive energy balance between the exported and imported energy from a building or a district within a specified time horizon. Research on NZPEBD encompasses all related aspects of energy in buildings and districts, starting from the definition of the basics of the concept, the boundary of the building/district, types of energy credits to be balanced, energy efficiency of the building envelope, integration of onsite renewable energy generation, technologies for short and long term storage, performance control and operational optimisation, onsite load-matching, offering flexibility to the grids, as well as people's acceptance and contribution and the economic feasibility.

Due to the importance of the NZPEBD topic, we opened a call for articles submission in a Special Issue "Net-Zero/Positive Energy Buildings and Districts"of the *Buildings* journal. This book is the collection of the articles published in that Special Issue. The book includes 17 research articles covering different aspects of NZPEBD planning, technologies, economics, building design, and retrofitting, citizen engagement, and collection of energy data.

We would like to thank the authors of the articles for their valuable contribution. We also wish to express our gratitude to the reviewers of the articles for their time and effort.

> **Ala Hasan and Francesco Reda** *Editors*
