<p> This work describes prison chaplains and chapel volunteers from three perspectives: (1) a historical perspective which is used to investigate the role of religion in prisons, (2) the chaplains&rsquo; perspective on the partnership between chaplains and chapel volunteers, and (3) the volunteers&rsquo; perspective on the predictors of volunteering in prison ministry. </p><p> First, the study provides a historical perspective on the role of prison ministry workers in prisons by examining: (a) the role of religion in the philanthropic life of John Howard, an eighteenth century prison reformer, (b) the role of religion in satisfying socio-economic pre-conditions that led to prison reform during the period of the Industrial Revolution, and (c) the role of religion during the development and evolution of the penal systems in the USA. </p><p> Second, the study explores the partnership between paid chaplains working for over three months at ten state, medium to high-level security, men&rsquo;s prisons in Indiana, and chapel volunteers providing in-person ministry work. The study is primarily based on in-person, in-depth interviews with 25 chaplains. Using modified analytic induction, the research leads to identification of four roles adopted by chaplains: Pastoral Counselor, Religious Coordinator, Administrative Minister, and Advocate for Prisoners. The study describes the partnership in general and explains how chaplains in each of these different roles perceive conflict and collaboration with volunteers. </p><p> Third, the study constructs a sampling frame consisting of an estimated 916 to 1,132 chapel volunteers working in the ten prisons. The study is based on responses to a survey based on a convenience sample of 106 of these volunteers. The study uses OLS regression to test 32 hypotheses. Among other things, the study finds that statistically significant predictors of higher amount and higher frequency of volunteering to prison ministry include: being retired, shorter length of commute to prison, tenure as prison ministry volunteer, lower motivation to develop and strengthen social ties, and higher frequency of attending religious services. </p><p> The work concludes with a summary and discussion of the findings, implications for theory and practitioners (including policymakers, prison administrators, chaplains, and volunteers), as well as limitations and suggestions for future research.</p>