A simple asymptotic approximation that describes the electromagnetic fields, currents, and voltages in a general microstrip transmission line problem is presented. Specifically, the transmission line equations relating the currents and voltages are established in a very efficient manner. Important properties of the capacitance and inductance matrices are established using elementary mathematics. These results and the equations are general enough to describe any number of microstrips, whose widths are allowed to vary in direction of propagation. When the widths are constant in this direction, another elementary asymptotic approximation shows that the electromagnetic fields are exponentially small away from the strips. This is, of course, the feature that makes them useful in guiding waves.