Many organs are composed of epithelial tubes that transport vital fluids. Such tubular organs develop in many different ways and generate tubes of widely varying sizes and structures, but always with the apical epithelial surface lining the lumen. We describe recent progress in several diverse cell culture and genetic models of tube morphogenesis, which suggest apical membrane biogenesis, vesicle fusion, and secretion play central roles in tube formation and growth. We propose a unifying mechanism of tube morphogenesis that has been modified to create tube diversity and describe how defects in the tube size-sensing step can lead to polycystic kidney disease.