This collection of scientific papers provides a state-of-the-art look at current knowledge on ocean worlds in our solar system and beyond. It is the result of a collaborative effort by scientists studying both terrestrial and extraterrestrial oceans, and analyzes the emergence of life and its survival on Earth as well as other potentially habitable planets and moons. The papers examine the more remote provinces of our solar system, focusing on the icy moons of the giant planets, like Europa and Titan, as well as bodies like Ceres and putative extrasolar ocean worlds. Their potential for subsurface liquid water oceans are explored, as is as their astrobiological potential. The collection also takes a look at Earth's own oceans, which offer important clues for the investigation of other ocean worlds. In addition, the collection addresses the outstanding key scientific questions and measurements, technologies and laboratory experiments necessary for the exploration of ocean worlds known today. Previously published in Space Science Reviews in the Topical Collection "Ocean Worlds"