**Abstract**

Thus far involuntary unemployment does not occur in Diamond-type Overlapping Generations models. In line with Keynesian macroeconomics, involuntary unemployment is traced back to aggregate demand failures. While macroeconomists majority refers aggregate demand failures to sticky prices, a minority attributes lacking aggregate demand to not perfectly flexible aggregate investment. The chapter investigates how an independent aggregate investment function causes involuntary unemployment under perfectly flexible competitive wage and interest rates in a Diamond-type neoclassical growth model with public debt and human capital accumulation. Moreover, it is shown that a higher public debt to output ratio enhances output growth and reduces involuntary unemployment.

**Keywords:** involuntary unemployment, overlapping generations models, inflexible aggregate investment, public debt, human capital accumulation
