A microfluidic system comprising: an actuator; and a microfluidic device comprising an enclosure, wherein said enclosure comprises: a flow region comprising a channel configured to contain a fluidic medium; and at least one chamber configured to contain said fluidic medium, said chamber fluidically connected to said flow region, wherein said chamber is a sequestration pen comprising: an isolation region; a connection region fluidically connecting said isolation region to said channel; and a well region comprising a deformable surface, wherein said deformable surface is disposed above said well region, and wherein said well region is fluidically connected to said isolation region; and wherein: said actuator is configured, upon being actuated, to deform said deformable surface, and when said flow region and said chamber are substantially filled with said fluidic medium, deformation of said deformable surface causes a flow of medium between said chamber and said flow region, and in the absence of said actuator being actuated, there is substantially no flow of medium between said channel and said isolation region of said sequestration pen. an actuator; and a microfluidic device comprising an enclosure, wherein said enclosure comprises: a flow region comprising a channel configured to contain a fluidic medium; and at least one chamber configured to contain said fluidic medium, said chamber fluidically connected to said flow region, wherein said chamber is a sequestration pen comprising: an isolation region; a connection region fluidically connecting said isolation region to said channel; and a well region comprising a deformable surface, wherein said deformable surface is disposed above said well region, and wherein said well region is fluidically connected to said isolation region; and wherein: said actuator is configured, upon being actuated, to deform said deformable surface, and when said flow region and said chamber are substantially filled with said fluidic medium, deformation of said deformable surface causes a flow of medium between said chamber and said flow region, and in the absence of said actuator being actuated, there is substantially no flow of medium between said channel and said isolation region of said sequestration pen. a flow region comprising a channel configured to contain a fluidic medium; and at least one chamber configured to contain said fluidic medium, said chamber fluidically connected to said flow region, wherein said chamber is a sequestration pen comprising: an isolation region; a connection region fluidically connecting said isolation region to said channel; and a well region comprising a deformable surface, wherein said deformable surface is disposed above said well region, and wherein said well region is fluidically connected to said isolation region; and wherein: said actuator is configured, upon being actuated, to deform said deformable surface, and when said flow region and said chamber are substantially filled with said fluidic medium, deformation of said deformable surface causes a flow of medium between said chamber and said flow region, and in the absence of said actuator being actuated, there is substantially no flow of medium between said channel and said isolation region of said sequestration pen. an isolation region; a connection region fluidically connecting said isolation region to said channel; and a well region comprising a deformable surface, wherein said deformable surface is disposed above said well region, and wherein said well region is fluidically connected to said isolation region; and wherein: said actuator is configured, upon being actuated, to deform said deformable surface, and when said flow region and said chamber are substantially filled with said fluidic medium, deformation of said deformable surface causes a flow of medium between said chamber and said flow region, and in the absence of said actuator being actuated, there is substantially no flow of medium between said channel and said isolation region of said sequestration pen. said actuator is configured, upon being actuated, to deform said deformable surface, and when said flow region and said chamber are substantially filled with said fluidic medium, deformation of said deformable surface causes a flow of medium between said chamber and said flow region, and in the absence of said actuator being actuated, there is substantially no flow of medium between said channel and said isolation region of said sequestration pen.