The paper presents two methods for passively breaking larger drops into precisely controlled smaller daughter drops using pressure-driven flow in simple microfluidic configurations: (i) a T junction and (ii) flow past isolated obstacles. The authors demonstrate that the T junction can achieve maximum precision in breaking droplets into daughter drops of a predetermined size ratio, while the obstacle-mediated breakup technique allows for the controlled change in drop size without increasing polydispersity. The critical conditions for drop breakup at the T junction are quantified, and an analytical model is developed to understand the transition from nonbreaking to breaking drops. The study also explores the asymmetric breakup of droplets by adjusting the relative lengths of the side channels. The techniques are validated through experiments using water droplets dispersed in hexadecane, achieving polydispersions of less than 5%. The findings have implications for precise control over droplet size and volume fraction in emulsions, which are crucial for applications such as micromixing and chemical reactions.The paper presents two methods for passively breaking larger drops into precisely controlled smaller daughter drops using pressure-driven flow in simple microfluidic configurations: (i) a T junction and (ii) flow past isolated obstacles. The authors demonstrate that the T junction can achieve maximum precision in breaking droplets into daughter drops of a predetermined size ratio, while the obstacle-mediated breakup technique allows for the controlled change in drop size without increasing polydispersity. The critical conditions for drop breakup at the T junction are quantified, and an analytical model is developed to understand the transition from nonbreaking to breaking drops. The study also explores the asymmetric breakup of droplets by adjusting the relative lengths of the side channels. The techniques are validated through experiments using water droplets dispersed in hexadecane, achieving polydispersions of less than 5%. The findings have implications for precise control over droplet size and volume fraction in emulsions, which are crucial for applications such as micromixing and chemical reactions.