Kaldor's Mattioli lectures analyse a two-sector model with increasing returns to scale (IRS) in industry and decreasing returns (DRS) in agriculture. This review article shows that (i) with IRS in industry a long-run equilibrium growth path with strictly positive growth rates may exist even if agriculture is subject to DRS; (ii) the industrial sector is the 'engine of growth' if agricultural investment is determined passively by available saving; (iii) if one introduces a separate agricultural investment function both positive and negative agricultural supply shocks may lead to stagnation, thus vindicating Kaldor's emphasis on commodity price stabilization.