In this talk I will describe the basic building blocks required to construct an effective numerical model to simulate propagating hydraulic fractures. I will discuss some of the unique the challenges faced when attempting to model propagating hydraulic fractures and some of the techniques that can be used to resolve these problems. I will demonstrate the efficacy of the models by comparison with analytic solutions and laboratory experiments. I will also discuss the challenges involved with extending the algorithms to enable the modeling of multiple simultaneously propagating hydraulic fractures.