Biological neurons use short and sudden increases in voltage to send information. These signals are more commonly known as action potentials, spikes or pulses. Recent neurological research has shown that neurons encode information in the timing of single spikes, and not only just in their average firing frequency. This paper gives an introduction to spiking neural networks, some biological background, and will present two models of spiking neurons that employ pulse coding. Networks of spiking neurons are more powerful than their non-spiking predecessors as they can encode temporal information in their signals, but therefore do also need different and biologically more plausible rules for synaptic plasticity.