A method, comprising: providing a first, inner fluid in a main microfluidic channel; flowing the first, inner fluid to a first intersection of the main microfluidic channel and a first side microfluidic channel containing a second, outer fluid to cause the first, inner fluid to become surrounded by the second, outer fluid without causing the first, inner fluid to form separate droplets prior to contact with a third, carrying fluid, wherein the first, inner fluid is immiscible with the second, outer fluid and the second, outer fluid is immiscible with the third, carrying fluid; flowing the first, inner fluid and the second, outer fluid to a second intersection of the main microfluidic channel and a second side microfluidic channel containing the third, carrying fluid to cause the second, outer fluid to become surrounded by the third, carrying fluid without causing the first, inner fluid and the second, outer fluid to form separate droplets, wherein the main microfluidic channel downstream of the second intersection has an average cross-sectional dimension between about 5% and about 20% larger than an average cross-sectional dimension of the main microfluidic channel upstream of the second intersection, relative to the average cross-sectional dimension of the main microfluidic channel upstream of the second intersection; and causing the first, inner fluid and the second, outer fluid to form individual droplets in a double emulsion, wherein in an outer fluidic droplet of the double emulsion, the first, inner fluid is contained within the second, outer fluid, and wherein the outer fluidic droplet is contained within the third, carrying fluid, wherein the double emulsion is generated by causing the first, inner fluid, the second, outer fluid, and the third, carrying fluid to leave the second intersection under jetting conditions, or under conditions such that a Weber number of the fluids is greater than 1, wherein the first, inner fluid and the second, outer fluid flow substantially collinearly prior to contact with the third, carrying fluid. providing a first, inner fluid in a main microfluidic channel; flowing the first, inner fluid to a first intersection of the main microfluidic channel and a first side microfluidic channel containing a second, outer fluid to cause the first, inner fluid to become surrounded by the second, outer fluid without causing the first, inner fluid to form separate droplets prior to contact with a third, carrying fluid, wherein the first, inner fluid is immiscible with the second, outer fluid and the second, outer fluid is immiscible with the third, carrying fluid; flowing the first, inner fluid and the second, outer fluid to a second intersection of the main microfluidic channel and a second side microfluidic channel containing the third, carrying fluid to cause the second, outer fluid to become surrounded by the third, carrying fluid without causing the first, inner fluid and the second, outer fluid to form separate droplets, wherein the main microfluidic channel downstream of the second intersection has an average cross-sectional dimension between about 5% and about 20% larger than an average cross-sectional dimension of the main microfluidic channel upstream of the second intersection, relative to the average cross-sectional dimension of the main microfluidic channel upstream of the second intersection; and causing the first, inner fluid and the second, outer fluid to form individual droplets in a double emulsion, wherein in an outer fluidic droplet of the double emulsion, the first, inner fluid is contained within the second, outer fluid, and wherein the outer fluidic droplet is contained within the third, carrying fluid, wherein the double emulsion is generated by causing the first, inner fluid, the second, outer fluid, and the third, carrying fluid to leave the second intersection under jetting conditions, or under conditions such that a Weber number of the fluids is greater than 1, wherein the first, inner fluid and the second, outer fluid flow substantially collinearly prior to contact with the third, carrying fluid.