Among the key questions that OVE’s 2015 review of the design and use of PBL explored were how the design and implementation of PBL operations changed over time and why countries demand PBL. The following sections will briefly summarize the review’s findings in this respect. OVE’s 2015 analysis did not seek to evaluate the achievements of the outcomes to which the PBL sought to contribute. It covered the period 1989–2014, with an emphasis on the last decade of the period.