Sustained economic growth requires a substantial and continuing investment in human capital. One major form of this investment is education. Education comprises various sectors including primary and secondary, college and university, noncredential forms of education, peer learning systems, job-related training, industry or state sponsored retraining, adult basic education, and basic literacy programs. A variety of different measures have been employed by economists to measure economic growth. The relationship between education and economic growth appears to be modest owing to a whole variety of factors including economic policies, political and social structures, and distribution of education. Human capital theory has been substantially reshaped in the latter part of the twentieth century in the light of these findings and the search for a comprehensive causative model continues.