A method for aligning sequences of streams comprising droplets in a microfluidic device, the method comprising: providing an emulsion comprising a plurality of target droplets and a plurality of tag droplets, wherein a said tag droplet comprises a first tag and a second tag; characterised in that the method comprises: splitting a said target droplet into a first target droplet and a second target droplet and splitting a said tag droplet into a first tag droplet and a second tag droplet, wherein both said first tag droplet and said second tag droplet comprise said first tag and said second tag, and wherein said splitting is performed using a droplet splitting module comprising an inlet channel, and a plurality of outlet channels; providing a said first target droplet and a said first tag droplet into a first stream of droplets, and providing a said second target droplet and a said second tag droplet into a second stream of droplets; detecting said first tag droplets and said first target droplets in said first stream and detecting said second tag droplets and said second target droplets in said second stream; determining a first sequence of droplets in said first stream based on said detection of said first tag droplets and said first target droplets, and determining a second sequence of droplets in said second stream based on said detection of said second tag droplets and said second target droplets; comparing said determined first and second sequences to align said first and second sequences; and identifying and selectively sorting a droplet in said second sequence using said aligned first and second sequences, wherein said sorting is performed using a droplet sorting module. providing an emulsion comprising a plurality of target droplets and a plurality of tag droplets, wherein a said tag droplet comprises a first tag and a second tag; characterised in that the method comprises: splitting a said target droplet into a first target droplet and a second target droplet and splitting a said tag droplet into a first tag droplet and a second tag droplet, wherein both said first tag droplet and said second tag droplet comprise said first tag and said second tag, and wherein said splitting is performed using a droplet splitting module comprising an inlet channel, and a plurality of outlet channels; providing a said first target droplet and a said first tag droplet into a first stream of droplets, and providing a said second target droplet and a said second tag droplet into a second stream of droplets; detecting said first tag droplets and said first target droplets in said first stream and detecting said second tag droplets and said second target droplets in said second stream; determining a first sequence of droplets in said first stream based on said detection of said first tag droplets and said first target droplets, and determining a second sequence of droplets in said second stream based on said detection of said second tag droplets and said second target droplets; comparing said determined first and second sequences to align said first and second sequences; and identifying and selectively sorting a droplet in said second sequence using said aligned first and second sequences, wherein said sorting is performed using a droplet sorting module. splitting a said target droplet into a first target droplet and a second target droplet and splitting a said tag droplet into a first tag droplet and a second tag droplet, wherein both said first tag droplet and said second tag droplet comprise said first tag and said second tag, and wherein said splitting is performed using a droplet splitting module comprising an inlet channel, and a plurality of outlet channels; providing a said first target droplet and a said first tag droplet into a first stream of droplets, and providing a said second target droplet and a said second tag droplet into a second stream of droplets; detecting said first tag droplets and said first target droplets in said first stream and detecting said second tag droplets and said second target droplets in said second stream; determining a first sequence of droplets in said first stream based on said detection of said first tag droplets and said first target droplets, and determining a second sequence of droplets in said second stream based on said detection of said second tag droplets and said second target droplets; comparing said determined first and second sequences to align said first and second sequences; and identifying and selectively sorting a droplet in said second sequence using said aligned first and second sequences, wherein said sorting is performed using a droplet sorting module.