While belief in God the Father, the Son and the Holy Spirit is at the very core of the Christian faith, the significance of the Spirit in particular is sometimes overlooked in faith practice and theological reflection, resulting in what theologians call Geistvergessenheit. In this context, Lumen Gentium, one of the most important documents of the Second Vatican Council (1962-1965), is usually praised for its pneumatological renewal. The current volume, however, argues that this renewal is no more than modest. The Holy Spirit is still conceived of predominantly as an adjunct to Christ. To substantiate that claim, Jos Moons has developed a novel method of close reading on the basis of which he compares Lumen gentium's conception of the Spirit to that of Mystici corporis (1943). He also analyses the redaction-historical development of the former and concludes with a plea to envisage the Spirit more boldly: as actively guiding the church, especially by means of the sensus fidelium, its charisms and the discernment of spirits.