Advanced research continues in the field of High Power Microwaves (HPM), which have potential applications ranging from long distance communications, radar, environmental waste clean up, bio‐toxin neutralization, fusion heating, as well as a host of others. Current HPM sources being studied are the Magnetically Insulated Line Oscillator, Relativistic Klystron Oscillator, and Relativistic Magnetron, and experimental and computational comparisons will be presented. Relevant components to be discussed are recent cathode results, recent antenna results, as well as the discussion of a HPM air breakdown experiment to be conducted in the near future. © 2003 American Institute of Physics