NULL Convention Logic (NCL) is a symbolically complete logic which expresses process completely in terms of the logic itself and inherently and conveniently expresses asynchronous digital circuits. The traditional form of Boolean logic is not symbolically complete in the sense that it requires the participation of a fundamentally different form of expression, time in the form of the clock, which has to be very carefully coordinated with the logic part of the expression to completely and effectively express a process. We introduce NULL Convention Logic in relation to Boolean logic as a four value logic, and as a three value logic and finally as two value logic quite different from traditional Boolean logic. We then show how systems can be constructed entirely in terms of NULL Convention Logic.