A number of primary studies and systematic reviews focused on the contribution of community health workers (CHWs) in the delivery of essential health services. In many countries, a cadre of informal health workers also provide services on a volunteer basis [community health volunteers (CHV)], but there has been no synthesis of studies investigating their role and potential contribution across a range of health conditions; most existing studies are narrowly focused on a single condition. As this cadre grows in importance, there is a need to examine the evidence on whether and how CHVs can improve access to and use of essential health services in low- and middle-income countries (LMICs). We report an umbrella review of systematic reviews, searching PubMed, the Cochrane library, the database of abstracts of reviews of effects (DARE), EMBASE, ProQuest dissertation and theses, the Campbell library and DOPHER. We considered a review as 'systematic' if it had an explicit search strategy with qualitative or quantitative summaries of data. We used the Joanna Briggs Institute (JBI) critical appraisal assessment checklist to assess methodological quality. A data extraction format prepared a priori was used to extract data. Findings were synthesized narratively. Of 422 records initially found by the search strategy, we identified 39 systematic reviews eligible for inclusion. Most concluded that services provided by CHVs were not inferior to those provided by other health workers, and sometimes better. However, CHVs performed less well in more complex tasks such as diagnosis and counselling. Their performance could be strengthened by regular supportive supervision, in-service training and adequate logistical support, as well as a high level of community ownership. The use of CHVs in the delivery of selected health services for population groups with limited access, particularly in LMICs, appears promising. However, success requires careful implementation, strong policy backing and continual support by their managers.