How Farmville turned the world into virtual farmers, why Steam's Summer Sale keeps gamers indoors all summer, how Netflix built a billion-dollar business on "binge-watching," and over 100 more examples of the psychology behind the most successful products ever created. Product Gems distils research from 84 behavioural science papers and case-studies into 108 bite-size "gems" that demonstrate the key techniques used by leading companies to build products people love.