This comparative theological study examines the experience of the Holy Spirit within Eastern Orthodox and Western Catholic Christian traditions. Written by Marie-Joseph Le Guillou, a theologian and member of the Chemin Neuf community, the work explores doctrinal differences and spiritual practices surrounding the Holy Spirit across these two major branches of Christianity. The book includes a preface by Olivier Clément and offers insights into how theological understanding shapes religious experience in both Eastern and Western contexts. Published in French, this concise volume contributes to ecumenical dialogue by highlighting both the shared foundations and distinctive approaches to pneumatology in Orthodox and Catholic theology.