A system for forming a plurality of sample-containing droplets suspended in a background fluid, comprising: a planar substrate having a top surface and a bottom surface; a sample well, a background fluid well, and a droplet outlet region selected from the group consisting of a pipette tip and a droplet well, a network of channels formed in the bottom surface of the substrate and fluidically interconnecting the sample well, the background fluid well, and the droplet outlet region; a droplet generation region defined by the network of channels and configured to generate sample-containing droplets suspended in the background fluid; and a planar sealing member forming a substantially flu id tight seal with the bottom surface of the substrate to make the network of channels fluid tight; wherein the droplet generation region is defined by the intersection of a first channel, a second channel, and a third channel; wherein the first channel is configured to transport sample-containing fluid from the sample well to the droplet generation region, the second channel is configured to transport background fluid from the background fluid well to the droplet generation region, and the third channel is configured to transport sample-containing droplets from the droplet generation region to the droplet outlet region; and characterized in that the sample well, the background fluid well and the droplet outlet region each comprise a well protrusion from the top surface of the substrate; and the sample well, the background fluid well, and the droplet outlet region have been integrally formed with the substrate by injection molding; and in that the first channel has a cross-section and includes an air trap configured to prevent sample-containing fluid from being inadvertently drawn through the first channel by capillary action, wherein in the air trap the cross-section of the first channel abruptly increases in one or more dimensions. a planar substrate having a top surface and a bottom surface; a sample well, a background fluid well, and a droplet outlet region selected from the group consisting of a pipette tip and a droplet well, a network of channels formed in the bottom surface of the substrate and fluidically interconnecting the sample well, the background fluid well, and the droplet outlet region; a droplet generation region defined by the network of channels and configured to generate sample-containing droplets suspended in the background fluid; and a planar sealing member forming a substantially flu id tight seal with the bottom surface of the substrate to make the network of channels fluid tight; wherein the droplet generation region is defined by the intersection of a first channel, a second channel, and a third channel; wherein the first channel is configured to transport sample-containing fluid from the sample well to the droplet generation region, the second channel is configured to transport background fluid from the background fluid well to the droplet generation region, and the third channel is configured to transport sample-containing droplets from the droplet generation region to the droplet outlet region; and characterized in that the sample well, the background fluid well and the droplet outlet region each comprise a well protrusion from the top surface of the substrate; and the sample well, the background fluid well, and the droplet outlet region have been integrally formed with the substrate by injection molding; and in that the first channel has a cross-section and includes an air trap configured to prevent sample-containing fluid from being inadvertently drawn through the first channel by capillary action, wherein in the air trap the cross-section of the first channel abruptly increases in one or more dimensions.