A Microgrid is an electrical distribution network consisted of distributed generators local loads and energy storage systems that can operate in grid connected or islanded modes. Different technologies are combined together such us power converters, control communications, optimization and so on. This way the energy can be generated and stored near to the consumption points improving the stability and reducing the losses produced by the large power lines. The speech will cover not only AC microgrids of conventional islanded systems to support AC loads are demanded in several areas such as islands rural and remote areas but also DC microgrids that may conform next low voltage distribution systems and microgrids will be based on DC since many generators storages and loads operate in DC such photovoltaics, batteries, supercapacitors, LEDs, laptops, and electronic equipment. Important aspect on microgrid research will be presented like modelling, control and operation, energy storage, standard based ICT and smart-metering, including wireless communications, power line communications, bus signaling, and so on. The application of smartmeters in microgrids will be highlighted. Energy Management Systems and Optimization, Online and offline optimization systems are required to enhance MicroGrid operation regarding energy price, power losses, and economical aspects. Advanced technologies like MultiAgent Systems, MAS, will be presented as powerful tool for distributed energy systems. Previous experiences in Danish electrical system like the Cell Controller project used MAS technologies to balance dispersed energy generation and consumption. Power quality aspects will be introduced, such as voltage and current harmonics and unbalances that have to be taken into account in a microgrid due to the existence of nonlinear and or single phase loads. In such a case, the coordination between power electronics converters is needed in order to enhance system power quality in a cooperative way. Many examples of real microgrid systems will be presented, such a demosite in Shanghai, China, a Smart Home living lab in Denmark, and so on. Finally, one important application in microgrids is maritime power systems, which include seaports, all and hybrid electrical ships, ferries and vessels.