Since 1965, indices of labor productivity have had a disappointing and largely unex plained performance. Not only is the rate of productivity growth over the post-1965 period lower than in preceding postwar years, but its upward trend has been broken at least twice. Since 1978, productivity growth has been effectively zero. If the trend of labor productivity from 1946-65 had continued until 1980, the current index would be about 15 percent above its actual level. Table 1 summarizes the postwar be havior of four alternative measures of pro ductivity.