Plant extracts have been utilized for treatment in medical conditions since ancient times. The decision to use these natural agents was initially supported only by empirical knowledge and/or common-sense. More recently, a body of scientific literature has been generated which confirms a biological basis for these types of medical effects. This book provides a summary of trends in biochemical/pharmacological research concerning seaweeds; an in-depth discussion of nutritional values and pharmaceutical effects of seaweed components and ecological factors responsible for altering algal systems and the possible anabolisms of these bioactive samples are described. The broad-range medicinal use of some seaweed components is reported as well.