In recent decades, alternatives to the established bubonic-plague theory have been presented as to the microbiologcal identity and mechanism(s) of spread of historical plague epidemics. In this monograph, the six important alternative theories are intensively discussed in the light of the historical sources, the central primary studies and standard works on bubonic plague and the alternative microbiological agents, insofar as they are testable. These seven theories are incompatible and at least six of them must be untenable. In the author's opinion, the arguments against the bubonic-plague...