From microscopic organisms on tidal rocks to dense marine forests, seaweeds vary widely in size and are amazingly well adapted to both the Arctic and the tropics. David Thomas presents a detailed look at what seaweeds are, how they live, and why humans value them.Thomas describes the red, brown, and green classifications of seaweeds that encompass more than ten thousand species. He explains how seaweeds get all of their nutrients from the surrounding water, needing roots only to anchor to the sea floor, and how some species use “anti-grazing” strategies to discourage fish by releasing swift doses of unappetizing acids. The economic value of seaweed is astounding. Some species are harvested for $1 billion annually, and seaweed constitutes up to ten percent of the average diet in Japan. The search continues for compounds in seaweed that may be beneficial as new drugs, antibiotics, and cancer treatments. Not only is seaweed vital to coastal ecosystems, but it is also an important part of everyday life.