Strontium-90, Gold-198, Cobalt-60, Iodine-131, Plutonium-238 -- all of these are isotopes capable of working for the betterment or destruction of mankind. This book is written as an explanation of the phrase ""peaceful uses of atomic energy"". Right now an army of isotopes is employed in hospitals, on farms, in industry. How they were discovered and put to use, what their roles are in all of these areas and what their future may be in 20th century life are the major points of discussion. It is largely a technical book written with the future scientist in mind though the highly curious student in other fields will be able to absorb much of the detail.