The "blue planet", Earth, with three quarters of its surface covered by oceans and seas, remains unexplored and undiscovered. This has relegated many marine species to undeserved exclusion, disregard or even contempt. A clear example of this is the seaweeds – "sea vegetables", as they are called in the media for their similarity to their land counterparts – a marine flora of great variety in size, shape and colour, with little awareness of their applications dating back to the dawn of civilization. They have been used in the East mainly as medicines and food, and have been venerated there for millennia. In the West, on the other hand, they have been reviled for their historical link to times of hunger and hardship, a view that fortunately has been changing in recent times. They are now on the menu in many restaurants and homes, thanks to their organoleptic and nutritional properties. The use of seaweeds for food is the main axis around which the different chapters in this book revolve and interlock.