The statement in Article 28 of the Reformed creed, the Belgic Confession, that all believers are in duty bound to join and unite themselves with an instituted church that has the three marks of a true church has proved to be controversial in Europe and in North America. The book that has recently occasioned this controversy over sound, creedal, Reformed doctrine and practice regarding the church is the RFPA publication, Bound to Join, authored by Prof. David J. Engelsma. A Defense of the Church Institute responds to the critics of Bound to Join and the despisers of the church institute. It defends the doctrine and practice of the church authoritatively confessed in Articles 27-29 of the Belgic Confession, demonstrating that love for the universal, invisible church of election will invariably express itself by love for the manifestation of this church in the true institute -- local congregation and denomination. This book also examines the growing movement that proposes and practices house church, finding the movement wanting. In the last chapter the book exposes the related error of the infamous radio Bible teacher, Harold Camping, that the church age has ended. Without concession or compromise, Engelsma reaffirms against the critics out of the true church institute with the offices of pastor, elder, and deacon there is no salvation. All believers, including the critics who presently sin against the faith by despising and rejecting the church institute, are bound to join.