In trying to foresee future trends, the surest approach is simply to project present trends forward assuming the future will resemble the past and present. This approach has not always worked well in the twentieth century. Two world wars interrupted a number of secular trends and the Great Depression of the 1930s reversed nearly all measures of economic progress. Ups and downs of the business cycle were anticipated on empirical and theoretical grounds, but the severity of the Depression and its effects, including political upheavals, were not. The early postwar period witnessed an utterly unexpected rise in fertility, the “baby boom,” which ended equally unexpectedly in the 1960s. The postwar economic boom exceeded expectations, its end in the early 1970s combining rising unemployment and inflation was not foreseen, nor was the recovery leading to the long continuing boom of the 1990s. Major technological inventions and their effects are almost by definition unforeseen.