This book explains that diffusion, osmosis, dissolution, evaporation, and heat loss all preferentially affect small bodies due to their high surface/volume ratios. Because surface area increases as the square of length, but volume (and mass) increase as the cube, large objects have low surface/volume ratios and small objects have high surface/volume ratios. This simple physical constraint governs much of the physical world. It accounts for why the Earth has active volcanoes, but the Moon does not, why the human brain has numerous folds, why deciduous trees lose their leaves every Fall, and why nanoparticles of gold melt at surprisingly low temperatures. It is a phenomenon well known to every scientist, but this book is the first comprehensive treatment of this effect.