Ronald James Sider (born 17 September 1939) is a Canadian-born American theologian and social activist.
He is the founder of Evangelicals for Social Action, a think-tank which seeks to develop biblical solutions to social and economic problems through incubating programs that operate at the intersection of faith and social justice.
He is a founding board member of the National Religious Partnership for the Environment.
He is also the Distinguished Professor of Theology, Holistic Ministry and Public Policy at Palmer Theological Seminary in Philadelphia, Pennsylvania.