The sub-series consists of the working files for special studies and evaluation reviews conducted by OED and its predecessor organization, the Operations Evaluation Unit (later Division) of the Programming and Budgeting Department, prior to the formation of sector-specific divisions in 1983. Reports include sector, country, management, and policy studies.

The series includes the first two evaluation studies conducted by the Operations Evaluation Unit. These studies included a deep study of everything the Bank had done in one country, Colombia, and a wide study evaluating loans to a number of countries in one sector, the electric power sector. The files for the first country study, Bank Operations in Colombia: An Evaluation, Report No. Z-18, 1972, also include a draft and final version of the 1975 Closing Report to Colombia Evaluation which was a follow-up review of the 1972 study to assess what progress had been made on the recommendations contained in the 1972 study. The files for the first sector study, Operations Evaluation Report: Electric Power, Report No. Z-17, 1972, include the 1975 follow-up report, Closing Report on Actions Relating to Recommendations of the Electric Power Evaluation Report of March 1972.

Other sector studies included in this series are: a comparative highway evaluation study; a Development Finance Companies study; a Bank lending for agriculture credit study; reviews of agricultural and rural development programs in Indonesia and the Philippines; and a review of rural development projects in Sub-Saharan Africa. The Department's first three management policy reviews are included and address delays in loan and credit effectiveness, delays in project preparation, and the role and use of consultants. Early operational policy reviews cover project implementation, supervision of Bank projects, and compliance with loan covenants. This series also includes files for OED studies of project monitoring and evaluation and technical assistance pilot evaluation studies conducted in Kenya and Afghanistan.

The study files in this series often contain earlier Bank documents, some dated as early as 1957, relating to the subject of the study. The compilers of these early studies established the practice of soliciting comments on draft studies and reports from all interested parties in the Bank and in the client countries, and most of these study files contain both a series of drafts and the related comments.