An apparatus (1) for mass producing monodisperse microbubbles, comprising a microfluidic flow focusing device (2) including a dispersed phase fluid supply channel (110) having an outlet (114) that discharges into a flow focusing junction (140); a continuous phase fluid supply channel (120, 120') having an outlet (124) that discharges into the flow focusing junction; and a bubble formation channel (130) having an inlet (132) disposed at the flow focusing junction. The configuration of the flow focusing junction (140) is such that, in operation, a flow of dispersed phase fluid (12) discharging from the outlet (114) of the dispersed phase fluid supply channel (110) is engageable in co-flow by a focusing flow of continuous phase fluid discharging from the outlet of the at least one continuous phase fluid supply channel under formation of a gradually thinning jet of dispersed phase fluid that extends into the inlet of the bubble formation channel.