The study has empirically examined the relative impact of public and private investment on economic growth and has also tested the crowding in or crowding out effect of public investment on private investment in four Southern African economies – Malawi, South Africa, Zambia and Zimbabwe. The analysis used annual time-series data covering the period from 1970 to 2014. The study provides new evidence to contribute firstly to the current debate regarding the relative importance of public and private investment in economic growth processes and secondly, on whether public investment crowds in or crowds out private investment in the selected countries. For this purpose, the study employed two empirical models using the recently developed Autoregressive Distributed Lag (ARDL)-bounds testing approach to cointegration. Model 1 examines the relative impact of public and private investment on economic growth while Model 2 investigates the crowding in or crowding out effect of gross public investment and its subcomponents (infrastructural and non-infrastructural) on private investment. The results of Model 1 largely supported the private investment-led economic growth strategy. In all the study countries, private investment had a positive impact on economic growth. Also, public investment positively contributed to economic growth in Zimbabwe, but in the remaining study countries, public investment had a negative relationship with economic growth. Results from Model 2 reveal that: (i) the crowding out effect of gross public investment on private investment predominates in the study countries; (ii) infrastructural public investment crowds in private investment in South Africa and Zimbabwe in the long run while it crowds out private investment in Malawi and Zambia in the short run; and (iii) non-infrastructural public investment crowds out private investment in South Africa and Zambia. On balance, the results from Model 2 show that public investment tends to crowd out private investment in the selected countries and this further underscore the importance of the private sector-led economic growth processes in the study countries. / Economics / D. Phil. (Economics)