One of the drawbacks to using an electron cyclotron resonance (ECR) plasma source in a production reactive ion etch tool is that, typically, the matching of the source load to the microwave power generator must be done manually, and hence is prone to error. This can lead to large variability in the power delivered to the plasma, that in turn may cause inconsistent etch results. In addition, if the reflected power due to mismatch between the generator and plasma is large enough, significant damage can be done to the equipment. This article documents an automated method for matching an ECR cavity to a microwave power generator. The algorithm is demonstrated on a Wavemat ECR high density source coupled to an AsTex S-1500i microwave power generator.