In this thesis, the droplet control methods by external forces were designed. The droplet separation, coalescence, splitting, capturing, and releasing techniques are essential for handing droplet-based experiment. First, optical forces were used to capture and coalesce the droplet. The optical trapping and coalescence steps were modeled theoretically and demonstrated experimentally. Calcium-Alginate gen was synthesized by colliding two droplets by capturing one droplet by the optical force. Also, acoustic radiation force was used to split droplets actively in the straight microchannel. The narrow SAW beam deflected the droplet surface and split into the two daughter droplets. The mechanism of the droplet splitting was discovered by estimating the acoustic radiation force on the droplets through the Ray acoustics regime. Polystyrene particles inside droplets could be positioned at specific droplet during the splitting procedure by acoustic radiation force acting on the particles. On the other hand, the SAW position and effective aperture can be controlled by tuning the SAW frequency. The droplets could be transferred to the target microwell inside the micro channel by tuning the location of the SAW beam. This technique is useful for a long term monitoring of a single cell in droplets.