Natural gas as a fuel for high and medium speed engines in industrial, power generation and marine propulsion applications is used for various reasons. Apart from the operating costs which are essentially determined by the fuel price, legislation is an important factor governing the use and the conception of the engines. The engine requirements are influenced by regulatory standards. Engine exhaust emission limits will continue to be stringent, including greenhouse relevant emissions such as CO2 and CH4. Additionally, a corresponding infrastructure is needed to guarantee the availability of the gas for the extensive implementation and use of gas engines. In the past, gas engine products were typically developed from production diesel engines. Today, gas engine development strategies are tailored to the intended use of these engines. Requirements concerning performance and emissions, fuel quality and fuel availability, transient response, etc. define the general technical specifications of the gas engine. These requirements provide the basis for the selection of the appropriate combustion concepts. Open chamber, prechamber with and without gas scavenging, and dual fuel concepts represent a broad variety of combustion concepts. Each of the mentioned systems entails individual characteristics and limitations and requires specific layouts of the engine design and fuel supply. This paper provides an overview of various gas engine concepts and development tools for high- and medium-speed gas engines.Copyright © 2014 by ASME