Droplet microfluidics is not simply a coalescence of “droplets” and “microfluidics”; beyond its role as an enabling technology, it also carries beautiful physics, and these factors have huge significance and implications for its future evolution. Droplet microfluidics has constantly found increasing influences across various disciplines. A good understanding of the fundaments of droplets in microfluidics apparently becomes an essential need. This chapter offers a brief tutorial on some fundamental aspects of droplets in microfluidics. Here, several basic concepts of capillarity are first introduced. And then, commonly used dimensionless numbers in microfluidics are presented and paraphrased. Next, conventional methods of droplet generation and size scaling of generated droplets are reviewed. Lastly, some key hydrodynamic issues of droplets flowing in microchannels are discussed.