For Christians, the Crucifixion of Jesus Christ is not merely a historical event; rather, it bears a significant theological dimension. Denying the Crucifixion is denying the defeat of death as it would still have the upper hand, but on the contrary, Christians do not fear death compared to those who do not believe in the Crucifixion and the Resurrection. Islam denies the Crucifixion, claiming that someone took Christ's form and was crucified in His stead (the Substitution Theory), while Christianity believes that Christ was truly crucified. This book confirms the Christian position and argues that the Islamic view was borrowed from the second century Gnostic/Docetic interpretation of the Crucifixion, attributed to Basilides of Alexandria. The purpose of this study is to investigate the extent to which the Islamic claim reflects the historical event. Methods used to achieve the conclusion are historical and systematic, as historical material and theological concepts are examined.