Microjoining with high energy density beams is a new subject in the sense that the progress of miniaturization in industry has made the desire to make microjoints rapidly and reliably a current and exciting topic. This article summarizes the current state of microjoining with both electron and laser beams. It considers the elementary physical processes such as heat and fluid flow to introduce the reader to the phenomena that affect melting, coalescence, and solidification needed for a successful microweld. The various forces driving (and resisting) fluid flow are analyzed. The article discusses the equipment suitable for microjoining and the metallurgical consequences and postweld metrology of the process. It also provides examples of developmental welds employing laser and electron beam microwelding techniques.