This thesis investigates the effects of micro-saving on the performance of microfinance institutions (MFIs) using unbalanced panels that straddle the period 2000-2012. This issue is also examined in a country-specific case study of Vietnam. There are four important findings. First, we found that serving more voluntary savers is costly and curtails depth of microfinance outreach. Second, micro-savings, in terms of the total deposits and the number of deposit accounts per staff member have a positive and significant impact on financial sustainability, cost-efficiency and breadth of outreach of MFIs. Third, a trade-off between financial sustainability and depth of outreach was found for deposit-taking MFIs, compared with MFIs that do not offer micro-savings financial products. Fourth, the findings from the cross-country studies are consistent with the findings from Vietnam. Overall, these findings have important implications for policy makers, microfinance practitioners and researchers.