Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online.The tandem bicycle or twin is a form of bicycle (occasionally, a tricycle) designed to be ridden by more than one person. The term tandem refers to the seating arrangement (fore to aft, not side-by-side) instead of the number of riders. A bike with two riders side-by-side is called a sociable. Patents related to tandem bicycles date from the late 1800s. In approximately 1898, Mikael Pedersen developed a tandem version of his Pedersen bicycle that weighed 24 pounds and a quad that weighed 64 pounds. Tandem popularity began to decline after WWII until Bill McReady at Santana Cycles instigated a revival. Modern technology has improved component and frame designs, and many tandems are as well-built as modern high-end road and off-road bikes.