Like so many others upon reaching adulthood, the author abandoned the fundamentalist church of his childhood and studying electronics and physics confirmed him in his belief that religious faith belonged to the past, and that science would ultimately be able to give all the answers and solve our problems. But that belief was seriously undermined by a 'synchronistic' experience during a skiing holiday in the French Vosges, which triggered his search for an answer by reading widely. He also experimented with a meditation technique and when pondering about several 'impossible' experiences during retreats he participated in, the pieces of life's puzzle suddenly fell together into their proper places. He is now convinced that religion (in the true sense of the word) is the most important pursuit we should be involved in. Using an ocean model in which the material world can be represented as waves on the surface of the ocean of the One, the many facts that cannot be accommodated within a scientific framework are explained. Many of these are described, supporting his claims with extensive quotations and references. He also discovered that many spiritual teachers have taught the same basic insight, viz. that the truth cannot be found by using our heads (investigating the ocean's surface 'horizontally'), but that we have to follow our hearts (explore the ocean's depths 'vertically'). So if you are just curious, or have a personal experience that cannot be fitted within the confines of a (horizontal) scientific framework, the book 'All is One' is Joop van Montfoort's answer to the question of 'How the pieces of life's puzzle fit together'. .