This paper reviews recent developments in micromachining technologies for the fabrication of microsensors, microactuators, and integrated microsystems, and discusses the requirements that micromachining technologies have to satisfy for many present and emerging applications. First, the paper discusses the challenges that micromachining technologies have to overcome and features that they have to provide for many future applications. Micromachining technologies have to be simple so that high yield and low cost can be achieved in manufacturing , they have to be capable of producing microstructures with a variety of shapes and sizes in all three dimensions, many of them have to be compatible with integration with electronics, they have to be capable of providing packaging and encapsulation at the wafer level for many devices that require operation in hermetic and/or vacuum environments, and finally they have to be capable of supporting a mixed set of materials, technologies and devices. Significant progress has been made in all of these areas during the past few years and several groups have developed new techniques that satisfy some or all of these requirements. The paper also reviews the most recent advances in the three mainstream technologies of bulk silicon micromachining, surface micromachining, and electroplating techniques. As microsystems become more complex, these three mainstream technologies will be increasingly used and combined to build complex systems at low cost.