This chapter discusses the analogy between microfluidic and electric circuits and the resistance increase brought by droplets in microfluidic channels. It describes different droplet-generation methods, including concepts for the accurate droplet creation at prescribed times, with certain size and at a certain distance. Microfluidic systems deal with the control and manipulation of small amounts of fluids in channels at micrometer scale. In continuous-flow-based lab-on-a-chips, the fluid flow in a microfluidic chip is controlled through integrated microvalves. When entering the microfluidic switch, the header droplet will always proceed along the primary outlet, as determined by the geometry of the switch. In [48], a flow-focusing geometry is used for the droplet generation. The proposed method requires the control of three channels: two input channels that contain the continuous and dispersed phases, respectively, and one output channel where a negative pressure is applied.