This work presents some ideas and theory on representing ordinary Petri nets using matrices and builds on previous work in [11],[12]. The three main types of matrices used for Petri net representation are the input, output and incidence matrices. The motivation for this work is that matrices can provide an alternative way to describe Petri nets from the conventional graphical representation. As is indicated several properties can be inferred, observed and derived from the matrices. Some definitions and examples are used.